1. 04 Jun, 2020 40 commits
    • Anshuman Khandual's avatar
      powerpc/mm: drop platform defined pmd_mknotpresent() · 124cb3a6
      Anshuman Khandual authored
      Patch series "mm/thp: Rename pmd_mknotpresent() as pmd_mknotvalid()", v2.
      
      This series renames pmd_mknotpresent() as pmd_mknotvalid().  Before that
      it drops an existing pmd_mknotpresent() definition from powerpc platform
      which was never required as it defines it's pmdp_invalidate() through
      subscribing __HAVE_ARCH_PMDP_INVALIDATE.  This does not create any
      functional change.
      
      This rename was suggested by Catalin during a previous discussion while we
      were trying to change the THP helpers on arm64 platform for migration.
      
      https://patchwork.kernel.org/patch/11019637/
      
      This patch (of 2):
      
      Platform needs to define pmd_mknotpresent() for generic pmdp_invalidate()
      only when __HAVE_ARCH_PMDP_INVALIDATE is not subscribed.  Otherwise
      platform specific pmd_mknotpresent() is not required.  Hence just drop it.
      Signed-off-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Vineet Gupta <vgupta@synopsys.com>
      Cc: Russell King <linux@armlinux.org.uk>
      Cc: Catalin Marinas <catalin.marinas@arm.com>
      Cc: Will Deacon <will@kernel.org>
      Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Dave Hansen <dave.hansen@linux.intel.com>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Link: http://lkml.kernel.org/r/1587520326-10099-1-git-send-email-anshuman.khandual@arm.com
      Link: http://lkml.kernel.org/r/1584680057-13753-1-git-send-email-anshuman.khandual@arm.com
      Link: http://lkml.kernel.org/r/1584680057-13753-2-git-send-email-anshuman.khandual@arm.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      124cb3a6
    • Yang Shi's avatar
      mm: thp: don't need to drain lru cache when splitting and mlocking THP · 67e4eb07
      Yang Shi authored
      Since commit 8f182270 ("mm/swap.c: flush lru pvecs on compound page
      arrival") THP would not stay in pagevec anymore.  So the optimization made
      by commit d9654322 ("thp: increase split_huge_page() success rate")
      doesn't make sense anymore, which tries to unpin munlocked THPs from
      pagevec by draining pagevec.
      
      Draining lru cache before isolating THP in mlock path is also unnecessary.
      b676b293 ("mm, thp: fix mapped pages avoiding unevictable list on
      mlock") added it and 9a73f61b ("thp, mlock: do not mlock PTE-mapped
      file huge pages") accidentally carried it over after the above
      optimization went in.
      Signed-off-by: default avatarYang Shi <yang.shi@linux.alibaba.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
      Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Link: http://lkml.kernel.org/r/1585946493-7531-1-git-send-email-yang.shi@linux.alibaba.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      67e4eb07
    • Shijie Hu's avatar
      hugetlbfs: get unmapped area below TASK_UNMAPPED_BASE for hugetlbfs · 88590253
      Shijie Hu authored
      In a 32-bit program, running on arm64 architecture.  When the address
      space below mmap base is completely exhausted, shmat() for huge pages will
      return ENOMEM, but shmat() for normal pages can still success on no-legacy
      mode.  This seems not fair.
      
      For normal pages, the calling trace of get_unmapped_area() is:
      
      	=> mm->get_unmapped_area()
      	if on legacy mode,
      		=> arch_get_unmapped_area()
      			=> vm_unmapped_area()
      	if on no-legacy mode,
      		=> arch_get_unmapped_area_topdown()
      			=> vm_unmapped_area()
      
      For huge pages, the calling trace of get_unmapped_area() is:
      
      	=> file->f_op->get_unmapped_area()
      		=> hugetlb_get_unmapped_area()
      			=> vm_unmapped_area()
      
      To solve this issue, we only need to make hugetlb_get_unmapped_area() take
      the same way as mm->get_unmapped_area().  Add *bottomup() and *topdown()
      for hugetlbfs, and check current mm->get_unmapped_area() to decide which
      one to use.  If mm->get_unmapped_area is equal to
      arch_get_unmapped_area_topdown(), hugetlb_get_unmapped_area() calls
      topdown routine, otherwise calls bottomup routine.
      Reported-by: default avatarkbuild test robot <lkp@intel.com>
      Signed-off-by: default avatarShijie Hu <hushijie3@huawei.com>
      Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Will Deacon <will@kernel.org>
      Cc: Xiaoming Ni <nixiaoming@huawei.com>
      Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
      Cc: yangerkun <yangerkun@huawei.com>
      Cc: ChenGang <cg.chen@huawei.com>
      Cc: Chen Jie <chenjie6@huawei.com>
      Link: http://lkml.kernel.org/r/20200518065338.113664-1-hushijie3@huawei.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      88590253
    • Mike Rapoport's avatar
      sparc32: register memory occupied by kernel as memblock.memory · 4360dfa9
      Mike Rapoport authored
      sparc32 never registered the memory occupied by the kernel image with
      memblock_add() and it only reserved this memory with meblock_reserve().
      
      With openbios as system firmware, the memory occupied by the kernel is
      reserved in openbios and removed from mem.available.  The prom setup code
      in the kernel uses mem.available to set up the memory banks and
      essentially there is a hole for the memory occupied by the kernel image.
      
      Later in bootmem_init() this memory is memblock_reserve()d.
      
      Up until recently, memmap initialization would call __init_single_page()
      for the pages in that hole, the free_low_memory_core_early() would mark
      them as reserved and everything would be Ok.
      
      After the change in memmap initialization introduced by the commit "mm:
      memmap_init: iterate over memblock regions rather that check each PFN",
      the hole is skipped and the page structs for it are not initialized.  And
      when they are passed from memblock to page allocator as reserved, the
      latter gets confused.
      
      Simply registering the memory occupied by the kernel with memblock_add()
      resolves this issue.
      
      Tested on qemu-system-sparc with Debian Etch [1] userspace.
      
      [1] https://people.debian.org/~aurel32/qemu/sparc/debian_etch_sparc_small.qcow2Signed-off-by: default avatarMike Rapoport <rppt@linux.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
      Cc: Guenter Roeck <linux@roeck-us.net>
      Link: https://lkml.kernel.org/r/20200517000050.GA87467@roeck-us.nlllllet/Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4360dfa9
    • chenqiwu's avatar
      include/linux/memblock.h: fix minor typo and unclear comment · 8cbd54f5
      chenqiwu authored
      Fix a minor typo "usabe->usable" for the current discription of member
      variable "memory" in struct memblock.
      
      BTW, I think it's unclear the member variable "base" in struct
      memblock_type is currently described as the physical address of memory
      region, change it to base address of the region is clearer since the
      variable is decorated as phys_addr_t.
      Signed-off-by: default avatarchenqiwu <chenqiwu@xiaomi.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarMike Rapoport <rppt@linux.ibm.com>
      Link: http://lkml.kernel.org/r/1588846952-32166-1-git-send-email-qiwuchen55@gmail.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8cbd54f5
    • Michal Hocko's avatar
      mm, mempolicy: fix up gup usage in lookup_node · 2d3a36a4
      Michal Hocko authored
      ba841078 ("mm/mempolicy: Allow lookup_node() to handle fatal signal")
      has added a special casing for 0 return value because that was a possible
      gup return value when interrupted by fatal signal.  This has been fixed by
      ae46d2aa ("mm/gup: Let __get_user_pages_locked() return -EINTR for
      fatal signal") in the mean time so ba841078 can be reverted.
      
      This patch however doesn't go all the way to revert it because the check
      for 0 is wrong and confusing here.  Firstly it is inherently unsafe to
      access the page when get_user_pages_locked returns 0 (aka no page
      returned).
      
      Fortunatelly this will not happen because get_user_pages_locked will not
      return 0 when nr_pages > 0 unless FOLL_NOWAIT is specified which is not
      the case here.  Document this potential error code in gup code while we
      are at it.
      Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Peter Xu <peterx@redhat.com>
      Link: http://lkml.kernel.org/r/20200421071026.18394-1-mhocko@kernel.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2d3a36a4
    • Changhee Han's avatar
      tools/vm/page_owner_sort.c: filter out unneeded line · 5b94ce2f
      Changhee Han authored
      To see a sorted result from page_owner, there must be a tiresome
      preprocessing step before running page_owner_sort.  This patch simply
      filters out lines which start with "PFN" while reading the page owner
      report.
      Signed-off-by: default avatarChanghee Han <ch0.han@lge.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Vlastimil Babka <vbabka@suse.cz>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Jonathan Corbet <corbet@lwn.net>
      Link: http://lkml.kernel.org/r/20200429052940.16968-1-ch0.han@lge.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5b94ce2f
    • Shakeel Butt's avatar
      mm: swap: memcg: fix memcg stats for huge pages · 21e330fc
      Shakeel Butt authored
      The commit 2262185c ("mm: per-cgroup memory reclaim stats") added
      PGLAZYFREE, PGACTIVATE & PGDEACTIVATE stats for cgroups but missed
      couple of places and PGLAZYFREE missed huge page handling. Fix that.
      Also for PGLAZYFREE use the irq-unsafe function to update as the irq is
      already disabled.
      
      Fixes: 2262185c ("mm: per-cgroup memory reclaim stats")
      Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Link: http://lkml.kernel.org/r/20200527182947.251343-1-shakeelb@google.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      21e330fc
    • Shakeel Butt's avatar
      mm: swap: fix vmstats for huge pages · 5d91f31f
      Shakeel Butt authored
      Many of the callbacks called by pagevec_lru_move_fn() does not correctly
      update the vmstats for huge pages. Fix that. Also __pagevec_lru_add_fn()
      use the irq-unsafe alternative to update the stat as the irqs are
      already disabled.
      Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Link: http://lkml.kernel.org/r/20200527182916.249910-1-shakeelb@google.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5d91f31f
    • Johannes Weiner's avatar
      mm: vmscan: limit the range of LRU type balancing · d483a5dd
      Johannes Weiner authored
      When LRU cost only shows up on one list, we abruptly stop scanning that
      list altogether.  That's an extreme reaction: by the time the other list
      starts thrashing and the pendulum swings back, we may have no recent age
      information on the first list anymore, and we could have significant
      latencies until the scanner has caught up.
      
      Soften this change in the feedback system by ensuring that no list
      receives less than a third of overall pressure, and only distribute the
      other 66% according to LRU cost.  This ensures that we maintain a minimum
      rate of aging on the entire workingset while it's being pressured, while
      still allowing a generous rate of convergence when the relative sizes of
      the lists need to adjust.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-15-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d483a5dd
    • Johannes Weiner's avatar
      mm: vmscan: reclaim writepage is IO cost · 96f8bf4f
      Johannes Weiner authored
      The VM tries to balance reclaim pressure between anon and file so as to
      reduce the amount of IO incurred due to the memory shortage.  It already
      counts refaults and swapins, but in addition it should also count
      writepage calls during reclaim.
      
      For swap, this is obvious: it's IO that wouldn't have occurred if the
      anonymous memory hadn't been under memory pressure.  From a relative
      balancing point of view this makes sense as well: even if anon is cold and
      reclaimable, a cache that isn't thrashing may have equally cold pages that
      don't require IO to reclaim.
      
      For file writeback, it's trickier: some of the reclaim writepage IO would
      have likely occurred anyway due to dirty expiration.  But not all of it -
      premature writeback reduces batching and generates additional writes.
      Since the flushers are already woken up by the time the VM starts writing
      cache pages one by one, let's assume that we'e likely causing writes that
      wouldn't have happened without memory pressure.  In addition, the per-page
      cost of IO would have probably been much cheaper if written in larger
      batches from the flusher thread rather than the single-page-writes from
      kswapd.
      
      For our purposes - getting the trend right to accelerate convergence on a
      stable state that doesn't require paging at all - this is sufficiently
      accurate.  If we later wanted to optimize for sustained thrashing, we can
      still refine the measurements.
      
      Count all writepage calls from kswapd as IO cost toward the LRU that the
      page belongs to.
      
      Why do this dynamically?  Don't we know in advance that anon pages require
      IO to reclaim, and so could build in a static bias?
      
      First, scanning is not the same as reclaiming.  If all the anon pages are
      referenced, we may not swap for a while just because we're scanning the
      anon list.  During this time, however, it's important that we age
      anonymous memory and the page cache at the same rate so that their
      hot-cold gradients are comparable.  Everything else being equal, we still
      want to reclaim the coldest memory overall.
      
      Second, we keep copies in swap unless the page changes.  If there is
      swap-backed data that's mostly read (tmpfs file) and has been swapped out
      before, we can reclaim it without incurring additional IO.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-14-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      96f8bf4f
    • Johannes Weiner's avatar
      mm: vmscan: determine anon/file pressure balance at the reclaim root · 7cf111bc
      Johannes Weiner authored
      We split the LRU lists into anon and file, and we rebalance the scan
      pressure between them when one of them begins thrashing: if the file cache
      experiences workingset refaults, we increase the pressure on anonymous
      pages; if the workload is stalled on swapins, we increase the pressure on
      the file cache instead.
      
      With cgroups and their nested LRU lists, we currently don't do this
      correctly.  While recursive cgroup reclaim establishes a relative LRU
      order among the pages of all involved cgroups, LRU pressure balancing is
      done on an individual cgroup LRU level.  As a result, when one cgroup is
      thrashing on the filesystem cache while a sibling may have cold anonymous
      pages, pressure doesn't get equalized between them.
      
      This patch moves LRU balancing decision to the root of reclaim - the same
      level where the LRU order is established.
      
      It does this by tracking LRU cost recursively, so that every level of the
      cgroup tree knows the aggregate LRU cost of all memory within its domain.
      When the page scanner calculates the scan balance for any given individual
      cgroup's LRU list, it uses the values from the ancestor cgroup that
      initiated the reclaim cycle.
      
      If one sibling is then thrashing on the cache, it will tip the pressure
      balance inside its ancestors, and the next hierarchical reclaim iteration
      will go more after the anon pages in the tree.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-13-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      7cf111bc
    • Johannes Weiner's avatar
      mm: balance LRU lists based on relative thrashing · 314b57fb
      Johannes Weiner authored
      Since the LRUs were split into anon and file lists, the VM has been
      balancing between page cache and anonymous pages based on per-list ratios
      of scanned vs.  rotated pages.  In most cases that tips page reclaim
      towards the list that is easier to reclaim and has the fewest actively
      used pages, but there are a few problems with it:
      
      1. Refaults and LRU rotations are weighted the same way, even though
         one costs IO and the other costs a bit of CPU.
      
      2. The less we scan an LRU list based on already observed rotations,
         the more we increase the sampling interval for new references, and
         rotations become even more likely on that list. This can enter a
         death spiral in which we stop looking at one list completely until
         the other one is all but annihilated by page reclaim.
      
      Since commit a528910e ("mm: thrash detection-based file cache sizing")
      we have refault detection for the page cache.  Along with swapin events,
      they are good indicators of when the file or anon list, respectively, is
      too small for its workingset and needs to grow.
      
      For example, if the page cache is thrashing, the cache pages need more
      time in memory, while there may be colder pages on the anonymous list.
      Likewise, if swapped pages are faulting back in, it indicates that we
      reclaim anonymous pages too aggressively and should back off.
      
      Replace LRU rotations with refaults and swapins as the basis for relative
      reclaim cost of the two LRUs.  This will have the VM target list balances
      that incur the least amount of IO on aggregate.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-12-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      314b57fb
    • Johannes Weiner's avatar
      mm: only count actual rotations as LRU reclaim cost · 264e90cc
      Johannes Weiner authored
      When shrinking the active file list we rotate referenced pages only when
      they're in an executable mapping.  The others get deactivated.  When it
      comes to balancing scan pressure, though, we count all referenced pages as
      rotated, even the deactivated ones.  Yet they do not carry the same cost
      to the system: the deactivated page *might* refault later on, but the
      deactivation is tangible progress toward freeing pages; rotations on the
      other hand cost time and effort without getting any closer to freeing
      memory.
      
      Don't treat both events as equal.  The following patch will hook up LRU
      balancing to cache and anon refaults, which are a much more concrete cost
      signal for reclaiming one list over the other.  Thus, remove the maybe-IO
      cost bias from page references, and only note the CPU cost for actual
      rotations that prevent the pages from getting reclaimed.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarMinchan Kim <minchan@kernel.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-11-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      264e90cc
    • Johannes Weiner's avatar
      mm: deactivations shouldn't bias the LRU balance · fbbb602e
      Johannes Weiner authored
      Operations like MADV_FREE, FADV_DONTNEED etc.  currently move any affected
      active pages to the inactive list to accelerate their reclaim (good) but
      also steer page reclaim toward that LRU type, or away from the other
      (bad).
      
      The reason why this is undesirable is that such operations are not part of
      the regular page aging cycle, and rather a fluke that doesn't say much
      about the remaining pages on that list; they might all be in heavy use,
      and once the chunk of easy victims has been purged, the VM continues to
      apply elevated pressure on those remaining hot pages.  The other LRU,
      meanwhile, might have easily reclaimable pages, and there was never a need
      to steer away from it in the first place.
      
      As the previous patch outlined, we should focus on recording actually
      observed cost to steer the balance rather than speculating about the
      potential value of one LRU list over the other.  In that spirit, leave
      explicitely deactivated pages to the LRU algorithm to pick up, and let
      rotations decide which list is the easiest to reclaim.
      
      [cai@lca.pw: fix set-but-not-used warning]
        Link: http://lkml.kernel.org/r/20200522133335.GA624@Qians-MacBook-Air.localSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarMinchan Kim <minchan@kernel.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Rik van Riel <riel@surriel.com>
      Cc: Qian Cai <cai@lca.pw>
      Link: http://lkml.kernel.org/r/20200520232525.798933-10-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      fbbb602e
    • Johannes Weiner's avatar
      mm: base LRU balancing on an explicit cost model · 1431d4d1
      Johannes Weiner authored
      Currently, scan pressure between the anon and file LRU lists is balanced
      based on a mixture of reclaim efficiency and a somewhat vague notion of
      "value" of having certain pages in memory over others.  That concept of
      value is problematic, because it has caused us to count any event that
      remotely makes one LRU list more or less preferrable for reclaim, even
      when these events are not directly comparable and impose very different
      costs on the system.  One example is referenced file pages that we still
      deactivate and referenced anonymous pages that we actually rotate back to
      the head of the list.
      
      There is also conceptual overlap with the LRU algorithm itself.  By
      rotating recently used pages instead of reclaiming them, the algorithm
      already biases the applied scan pressure based on page value.  Thus, when
      rebalancing scan pressure due to rotations, we should think of reclaim
      cost, and leave assessing the page value to the LRU algorithm.
      
      Lastly, considering both value-increasing as well as value-decreasing
      events can sometimes cause the same type of event to be counted twice,
      i.e.  how rotating a page increases the LRU value, while reclaiming it
      succesfully decreases the value.  In itself this will balance out fine,
      but it quietly skews the impact of events that are only recorded once.
      
      The abstract metric of "value", the murky relationship with the LRU
      algorithm, and accounting both negative and positive events make the
      current pressure balancing model hard to reason about and modify.
      
      This patch switches to a balancing model of accounting the concrete,
      actually observed cost of reclaiming one LRU over another.  For now, that
      cost includes pages that are scanned but rotated back to the list head.
      Subsequent patches will add consideration for IO caused by refaulting of
      recently evicted pages.
      
      Replace struct zone_reclaim_stat with two cost counters in the lruvec, and
      make everything that affects cost go through a new lru_note_cost()
      function.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-9-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      1431d4d1
    • Johannes Weiner's avatar
      mm: vmscan: drop unnecessary div0 avoidance rounding in get_scan_count() · a4fe1631
      Johannes Weiner authored
      When we calculate the relative scan pressure between the anon and file LRU
      lists, we have to assume that reclaim_stat can contain zeroes.  To avoid
      div0 crashes, we add 1 to all denominators like so:
      
              anon_prio = swappiness;
              file_prio = 200 - anon_prio;
      
      	[...]
      
              /*
               * The amount of pressure on anon vs file pages is inversely
               * proportional to the fraction of recently scanned pages on
               * each list that were recently referenced and in active use.
               */
              ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
              ap /= reclaim_stat->recent_rotated[0] + 1;
      
              fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
              fp /= reclaim_stat->recent_rotated[1] + 1;
              spin_unlock_irq(&pgdat->lru_lock);
      
              fraction[0] = ap;
              fraction[1] = fp;
              denominator = ap + fp + 1;
      
      While reclaim_stat can contain 0, it's not actually possible for ap + fp
      to be 0.  One of anon_prio or file_prio could be zero, but they must still
      add up to 200.  And the reclaim_stat fraction, due to the +1 in there, is
      always at least 1.  So if one of the two numerators is 0, the other one
      can't be.  ap + fp is always at least 1.  Drop the + 1.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-8-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a4fe1631
    • Johannes Weiner's avatar
      mm: remove use-once cache bias from LRU balancing · 96824687
      Johannes Weiner authored
      When the splitlru patches divided page cache and swap-backed pages into
      separate LRU lists, the pressure balance between the lists was biased to
      account for the fact that streaming IO can cause memory pressure with a
      flood of pages that are used only once.  New page cache additions would
      tip the balance toward the file LRU, and repeat access would neutralize
      that bias again.  This ensured that page reclaim would always go for
      used-once cache first.
      
      Since e9868505 ("mm,vmscan: only evict file pages when we have
      plenty"), page reclaim generally skips over swap-backed memory entirely as
      long as there is used-once cache present, and will apply the LRU balancing
      when only repeatedly accessed cache pages are left - at which point the
      previous use-once bias will have been neutralized.  This makes the
      use-once cache balancing bias unnecessary.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Acked-by: default avatarMinchan Kim <minchan@kernel.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-7-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      96824687
    • Johannes Weiner's avatar
      mm: workingset: let cache workingset challenge anon · 34e58cac
      Johannes Weiner authored
      We activate cache refaults with reuse distances in pages smaller than the
      size of the total cache.  This allows new pages with competitive access
      frequencies to establish themselves, as well as challenge and potentially
      displace pages on the active list that have gone cold.
      
      However, that assumes that active cache can only replace other active
      cache in a competition for the hottest memory.  This is not a great
      default assumption.  The page cache might be thrashing while there are
      enough completely cold and unused anonymous pages sitting around that we'd
      only have to write to swap once to stop all IO from the cache.
      
      Activate cache refaults when their reuse distance in pages is smaller than
      the total userspace workingset, including anonymous pages.
      
      Reclaim can still decide how to balance pressure among the two LRUs
      depending on the IO situation.  Rotational drives will prefer avoiding
      random IO from swap and go harder after cache.  But fundamentally, hot
      cache should be able to compete with anon pages for a place in RAM.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-6-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      34e58cac
    • Johannes Weiner's avatar
      mm: fold and remove lru_cache_add_anon() and lru_cache_add_file() · 6058eaec
      Johannes Weiner authored
      They're the same function, and for the purpose of all callers they are
      equivalent to lru_cache_add().
      
      [akpm@linux-foundation.org: fix it for local_lock changes]
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarRik van Riel <riel@surriel.com>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Acked-by: default avatarMinchan Kim <minchan@kernel.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-5-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      6058eaec
    • Johannes Weiner's avatar
      mm: allow swappiness that prefers reclaiming anon over the file workingset · c843966c
      Johannes Weiner authored
      With the advent of fast random IO devices (SSDs, PMEM) and in-memory swap
      devices such as zswap, it's possible for swap to be much faster than
      filesystems, and for swapping to be preferable over thrashing filesystem
      caches.
      
      Allow setting swappiness - which defines the rough relative IO cost of
      cache misses between page cache and swap-backed pages - to reflect such
      situations by making the swap-preferred range configurable.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-4-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c843966c
    • Johannes Weiner's avatar
      mm: keep separate anon and file statistics on page reclaim activity · 497a6c1b
      Johannes Weiner authored
      Having statistics on pages scanned and pages reclaimed for both anon and
      file pages makes it easier to evaluate changes to LRU balancing.
      
      While at it, clean up the stat-keeping mess for isolation, putback,
      reclaim stats etc.  a bit: first the physical LRU operation (isolation and
      putback), followed by vmstats, reclaim_stats, and then vm events.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Rik van Riel <riel@surriel.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-3-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      497a6c1b
    • Johannes Weiner's avatar
      mm: fix LRU balancing effect of new transparent huge pages · 5df74196
      Johannes Weiner authored
      The reclaim code that balances between swapping and cache reclaim tries to
      predict likely reuse based on in-memory reference patterns alone.  This
      works in many cases, but when it fails it cannot detect when the cache is
      thrashing pathologically, or when we're in the middle of a swap storm.
      
      The high seek cost of rotational drives under which the algorithm evolved
      also meant that mistakes could quickly result in lockups from too
      aggressive swapping (which is predominantly random IO).  As a result, the
      balancing code has been tuned over time to a point where it mostly goes
      for page cache and defers swapping until the VM is under significant
      memory pressure.
      
      The resulting strategy doesn't make optimal caching decisions - where
      optimal is the least amount of IO required to execute the workload.
      
      The proliferation of fast random IO devices such as SSDs, in-memory
      compression such as zswap, and persistent memory technologies on the
      horizon, has made this undesirable behavior very noticable: Even in the
      presence of large amounts of cold anonymous memory and a capable swap
      device, the VM refuses to even seriously scan these pages, and can leave
      the page cache thrashing needlessly.
      
      This series sets out to address this.  Since commit ("a528910e mm:
      thrash detection-based file cache sizing") we have exact tracking of
      refault IO - the ultimate cost of reclaiming the wrong pages.  This allows
      us to use an IO cost based balancing model that is more aggressive about
      scanning anonymous memory when the cache is thrashing, while being able to
      avoid unnecessary swap storms.
      
      These patches base the LRU balance on the rate of refaults on each list,
      times the relative IO cost between swap device and filesystem
      (swappiness), in order to optimize reclaim for least IO cost incurred.
      
      	History
      
      I floated these changes in 2016.  At the time they were incomplete and
      full of workarounds due to a lack of infrastructure in the reclaim code:
      We didn't have PageWorkingset, we didn't have hierarchical cgroup
      statistics, and problems with the cgroup swap controller.  As swapping
      wasn't too high a priority then, the patches stalled out.  With all
      dependencies in place now, here we are again with much cleaner,
      feature-complete patches.
      
      I kept the acks for patches that stayed materially the same :-)
      
      Below is a series of test results that demonstrate certain problematic
      behavior of the current code, as well as showcase the new code's more
      predictable and appropriate balancing decisions.
      
      	Test #1: No convergence
      
      This test shows an edge case where the VM currently doesn't converge at
      all on a new file workingset with a stale anon/tmpfs set.
      
      The test sets up a cold anon set the size of 3/4 RAM, then tries to
      establish a new file set half the size of RAM (flat access pattern).
      
      The vanilla kernel refuses to even scan anon pages and never converges.
      The file set is perpetually served from the filesystem.
      
      The first test kernel is with the series up to the workingset patch
      applied.  This allows thrashing page cache to challenge the anonymous
      workingset.  The VM then scans the lists based on the current
      scanned/rotated balancing algorithm.  It converges on a stable state where
      all cold anon pages are pushed out and the fileset is served entirely from
      cache:
      
      			    noconverge/5.7-rc5-mm	noconverge/5.7-rc5-mm-workingset
      Scanned			417719308.00 (    +0.00%)		64091155.00 (   -84.66%)
      Reclaimed		417711094.00 (    +0.00%)		61640308.00 (   -85.24%)
      Reclaim efficiency %	      100.00 (    +0.00%)		      96.18 (    -3.78%)
      Scanned file		417719308.00 (    +0.00%)		59211118.00 (   -85.83%)
      Scanned anon			0.00 (    +0.00%)	         4880037.00 (          )
      Swapouts			0.00 (    +0.00%)	         2439957.00 (          )
      Swapins				0.00 (    +0.00%)		     257.00 (          )
      Refaults		415246605.00 (    +0.00%)		59183722.00 (   -85.75%)
      Restore refaults		0.00 (    +0.00%)	        54988252.00 (          )
      
      The second test kernel is with the full patch series applied, which
      replaces the scanned/rotated ratios with refault/swapin rate-based
      balancing.  It evicts the cold anon pages more aggressively in the
      presence of a thrashing cache and the absence of swapins, and so converges
      with about 60% of the IO and reclaim activity:
      
      			noconverge/5.7-rc5-mm-workingset	noconverge/5.7-rc5-mm-lrubalance
      Scanned				64091155.00 (    +0.00%)		37579741.00 (   -41.37%)
      Reclaimed			61640308.00 (    +0.00%)		35129293.00 (   -43.01%)
      Reclaim efficiency %		      96.18 (    +0.00%)		      93.48 (    -2.78%)
      Scanned file			59211118.00 (    +0.00%)		32708385.00 (   -44.76%)
      Scanned anon			 4880037.00 (    +0.00%)		 4871356.00 (    -0.18%)
      Swapouts			 2439957.00 (    +0.00%)		 2435565.00 (    -0.18%)
      Swapins				     257.00 (    +0.00%)		     262.00 (    +1.94%)
      Refaults			59183722.00 (    +0.00%)		32675667.00 (   -44.79%)
      Restore refaults		54988252.00 (    +0.00%)		28480430.00 (   -48.21%)
      
      We're triggering this case in host sideloading scenarios: When a host's
      primary workload is not saturating the machine (primary load is usually
      driven by user activity), we can optimistically sideload a batch job; if
      user activity picks up and the primary workload needs the whole host
      during this time, we freeze the sideload and rely on it getting pushed to
      swap.  Frequently that swapping doesn't happen and the completely inactive
      sideload simply stays resident while the expanding primary worklad is
      struggling to gain ground.
      
      	Test #2: Kernel build
      
      This test is a a kernel build that is slightly memory-restricted (make -j4
      inside a 400M cgroup).
      
      Despite the very aggressive swapping of cold anon pages in test #1, this
      test shows that the new kernel carefully balances swap against cache
      refaults when both the file and the cache set are pressured.
      
      It shows the patched kernel to be slightly better at finding the coldest
      memory from the combined anon and file set to evict under pressure.  The
      result is lower aggregate reclaim and paging activity:
      
      z				    5.7-rc5-mm	5.7-rc5-mm-lrubalance
      Real time		   210.60 (    +0.00%)	   210.97 (    +0.18%)
      User time		   745.42 (    +0.00%)	   746.48 (    +0.14%)
      System time		    69.78 (    +0.00%)	    69.79 (    +0.02%)
      Scanned file		354682.00 (    +0.00%)	293661.00 (   -17.20%)
      Scanned anon		465381.00 (    +0.00%)	378144.00 (   -18.75%)
      Swapouts		185920.00 (    +0.00%)	147801.00 (   -20.50%)
      Swapins			 34583.00 (    +0.00%)	 32491.00 (    -6.05%)
      Refaults		212664.00 (    +0.00%)	172409.00 (   -18.93%)
      Restore refaults	 48861.00 (    +0.00%)	 80091.00 (   +63.91%)
      Total paging IO		433167.00 (    +0.00%)	352701.00 (   -18.58%)
      
      	Test #3: Overload
      
      This next test is not about performance, but rather about the
      predictability of the algorithm.  The current balancing behavior doesn't
      always lead to comprehensible results, which makes performance analysis
      and parameter tuning (swappiness e.g.) very difficult.
      
      The test shows the balancing behavior under equivalent anon and file
      input.  Anon and file sets are created of equal size (3/4 RAM), have the
      same access patterns (a hot-cold gradient), and synchronized access rates.
      Swappiness is raised from the default of 60 to 100 to indicate equal IO
      cost between swap and cache.
      
      With the vanilla balancing code, anon scans make up around 9% of the total
      pages scanned, or a ~1:10 ratio.  This is a surprisingly skewed ratio, and
      it's an outcome that is hard to explain given the input parameters to the
      VM.
      
      The new balancing model targets a 1:2 balance: All else being equal,
      reclaiming a file page costs one page IO - the refault; reclaiming an anon
      page costs two IOs - the swapout and the swapin.  In the test we observe a
      ~1:3 balance.
      
      The scanned and paging IO numbers indicate that the anon LRU algorithm we
      have in place right now does a slightly worse job at picking the coldest
      pages compared to the file algorithm.  There is ongoing work to improve
      this, like Joonsoo's anon workingset patches; however, it's difficult to
      compare the two aging strategies when the balancing between them is
      behaving unintuitively.
      
      The slightly less efficient anon reclaim results in a deviation from the
      optimal 1:2 scan ratio we would like to see here - however, 1:3 is much
      closer to what we'd want to see in this test than the vanilla kernel's
      aging of 10+ cache pages for every anonymous one:
      
      			overload-100/5.7-rc5-mm-workingset	overload-100/5.7-rc5-mm-lrubalance-realfile
      Scanned				 533633725.00 (    +0.00%)			  595687785.00 (   +11.63%)
      Reclaimed			 494325440.00 (    +0.00%)			  518154380.00 (    +4.82%)
      Reclaim efficiency %			92.63 (    +0.00%)				 86.98 (    -6.03%)
      Scanned file			 484532894.00 (    +0.00%)			  456937722.00 (    -5.70%)
      Scanned anon			  49100831.00 (    +0.00%)			  138750063.00 (  +182.58%)
      Swapouts			   8096423.00 (    +0.00%)			   48982142.00 (  +504.98%)
      Swapins				  10027384.00 (    +0.00%)			   62325044.00 (  +521.55%)
      Refaults			 479819973.00 (    +0.00%)			  451309483.00 (    -5.94%)
      Restore refaults		 426422087.00 (    +0.00%)			  399914067.00 (    -6.22%)
      Total paging IO			 497943780.00 (    +0.00%)			  562616669.00 (   +12.99%)
      
      	Test #4: Parallel IO
      
      It's important to note that these patches only affect the situation where
      the kernel has to reclaim workingset memory, which is usually a
      transitionary period.  The vast majority of page reclaim occuring in a
      system is from trimming the ever-expanding page cache.
      
      These patches don't affect cache trimming behavior.  We never swap as long
      as we only have use-once cache moving through the file LRU, we only
      consider swapping when the cache is actively thrashing.
      
      The following test demonstrates this.  It has an anon workingset that
      takes up half of RAM and then writes a file that is twice the size of RAM
      out to disk.
      
      As the cache is funneled through the inactive file list, no anon pages are
      scanned (aside from apparently some background noise of 10 pages):
      
      					  5.7-rc5-mm		          5.7-rc5-mm-lrubalance
      Scanned			    10714722.00 (    +0.00%)		       10723445.00 (    +0.08%)
      Reclaimed		    10703596.00 (    +0.00%)		       10712166.00 (    +0.08%)
      Reclaim efficiency %		  99.90 (    +0.00%)			     99.89 (    -0.00%)
      Scanned file		    10714722.00 (    +0.00%)		       10723435.00 (    +0.08%)
      Scanned anon			   0.00 (    +0.00%)			     10.00 (          )
      Swapouts			   0.00 (    +0.00%)			      7.00 (          )
      Swapins				   0.00 (    +0.00%)			      0.00 (    +0.00%)
      Refaults			  92.00 (    +0.00%)			     41.00 (   -54.84%)
      Restore refaults		   0.00 (    +0.00%)			      0.00 (    +0.00%)
      Total paging IO			  92.00 (    +0.00%)			     48.00 (   -47.31%)
      
      This patch (of 14):
      
      Currently, THP are counted as single pages until they are split right
      before being swapped out.  However, at that point the VM is already in the
      middle of reclaim, and adjusting the LRU balance then is useless.
      
      Always account THP by the number of basepages, and remove the fixup from
      the splitting path.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarRik van Riel <riel@surriel.com>
      Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Acked-by: default avatarMinchan Kim <minchan@kernel.org>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Link: http://lkml.kernel.org/r/20200520232525.798933-1-hannes@cmpxchg.org
      Link: http://lkml.kernel.org/r/20200520232525.798933-2-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5df74196
    • Johannes Weiner's avatar
      mm: memcontrol: update page->mem_cgroup stability rules · a0b5b414
      Johannes Weiner authored
      The previous patches have simplified the access rules around
      page->mem_cgroup somewhat:
      
      1. We never change page->mem_cgroup while the page is isolated by
         somebody else.  This was by far the biggest exception to our rules and
         it didn't stop at lock_page() or lock_page_memcg().
      
      2. We charge pages before they get put into page tables now, so the
         somewhat fishy rule about "can be in page table as long as it's still
         locked" is now gone and boiled down to having an exclusive reference to
         the page.
      
      Document the new rules.  Any of the following will stabilize the
      page->mem_cgroup association:
      
      - the page lock
      - LRU isolation
      - lock_page_memcg()
      - exclusive access to the page
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-20-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a0b5b414
    • Johannes Weiner's avatar
      mm: memcontrol: delete unused lrucare handling · d9eb1ea2
      Johannes Weiner authored
      Swapin faults were the last event to charge pages after they had already
      been put on the LRU list.  Now that we charge directly on swapin, the
      lrucare portion of the charge code is unused.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-19-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d9eb1ea2
    • Alex Shi's avatar
      mm: memcontrol: document the new swap control behavior · 0a27cae1
      Alex Shi authored
      Signed-off-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-18-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      0a27cae1
    • Johannes Weiner's avatar
      mm: memcontrol: charge swapin pages on instantiation · 4c6355b2
      Johannes Weiner authored
      Right now, users that are otherwise memory controlled can easily escape
      their containment and allocate significant amounts of memory that they're
      not being charged for.  That's because swap readahead pages are not being
      charged until somebody actually faults them into their page table.  This
      can be exploited with MADV_WILLNEED, which triggers arbitrary readahead
      allocations without charging the pages.
      
      There are additional problems with the delayed charging of swap pages:
      
      1. To implement refault/workingset detection for anonymous pages, we
         need to have a target LRU available at swapin time, but the LRU is not
         determinable until the page has been charged.
      
      2. To implement per-cgroup LRU locking, we need page->mem_cgroup to be
         stable when the page is isolated from the LRU; otherwise, the locks
         change under us.  But swapcache gets charged after it's already on the
         LRU, and even if we cannot isolate it ourselves (since charging is not
         exactly optional).
      
      The previous patch ensured we always maintain cgroup ownership records for
      swap pages.  This patch moves the swapcache charging point from the fault
      handler to swapin time to fix all of the above problems.
      
      v2: simplify swapin error checking (Joonsoo)
      
      [hughd@google.com: fix livelock in __read_swap_cache_async()]
        Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2005212246080.8458@eggly.anvilsSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarHugh Dickins <hughd@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Cc: Rafael Aquini <aquini@redhat.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-17-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4c6355b2
    • Johannes Weiner's avatar
      mm: memcontrol: make swap tracking an integral part of memory control · 2d1c4980
      Johannes Weiner authored
      Without swap page tracking, users that are otherwise memory controlled can
      easily escape their containment and allocate significant amounts of memory
      that they're not being charged for.  That's because swap does readahead,
      but without the cgroup records of who owned the page at swapout, readahead
      pages don't get charged until somebody actually faults them into their
      page table and we can identify an owner task.  This can be maliciously
      exploited with MADV_WILLNEED, which triggers arbitrary readahead
      allocations without charging the pages.
      
      Make swap swap page tracking an integral part of memcg and remove the
      Kconfig options.  In the first place, it was only made configurable to
      allow users to save some memory.  But the overhead of tracking cgroup
      ownership per swap page is minimal - 2 byte per page, or 512k per 1G of
      swap, or 0.04%.  Saving that at the expense of broken containment
      semantics is not something we should present as a coequal option.
      
      The swapaccount=0 boot option will continue to exist, and it will
      eliminate the page_counter overhead and hide the swap control files, but
      it won't disable swap slot ownership tracking.
      
      This patch makes sure we always have the cgroup records at swapin time;
      the next patch will fix the actual bug by charging readahead swap pages at
      swapin time rather than at fault time.
      
      v2: fix double swap charge bug in cgroup1/cgroup2 code gating
      
      [hannes@cmpxchg.org: fix crash with cgroup_disable=memory]
        Link: http://lkml.kernel.org/r/20200521215855.GB815153@cmpxchg.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
      Link: http://lkml.kernel.org/r/20200508183105.225460-16-hannes@cmpxchg.orgDebugged-by: default avatarHugh Dickins <hughd@google.com>
      Debugged-by: default avatarMichal Hocko <mhocko@kernel.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2d1c4980
    • Johannes Weiner's avatar
      mm: memcontrol: prepare swap controller setup for integration · eccb52e7
      Johannes Weiner authored
      A few cleanups to streamline the swap controller setup:
      
      - Replace the do_swap_account flag with cgroup_memory_noswap. This
        brings it in line with other functionality that is usually available
        unless explicitly opted out of - nosocket, nokmem.
      
      - Remove the really_do_swap_account flag that stores the boot option
        and is later used to switch the do_swap_account. It's not clear why
        this indirection is/was necessary. Use do_swap_account directly.
      
      - Minor coding style polishing
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-15-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      eccb52e7
    • Johannes Weiner's avatar
      mm: memcontrol: drop unused try/commit/cancel charge API · f0e45fb4
      Johannes Weiner authored
      There are no more users. RIP in peace.
      
      [arnd@arndb.de: fix an unused-function warning]
        Link: http://lkml.kernel.org/r/20200528095640.151454-1-arnd@arndb.deSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-14-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      f0e45fb4
    • Johannes Weiner's avatar
      mm: memcontrol: convert anon and file-thp to new mem_cgroup_charge() API · 9d82c694
      Johannes Weiner authored
      With the page->mapping requirement gone from memcg, we can charge anon and
      file-thp pages in one single step, right after they're allocated.
      
      This removes two out of three API calls - especially the tricky commit
      step that needed to happen at just the right time between when the page is
      "set up" and when it's "published" - somewhat vague and fluid concepts
      that varied by page type.  All we need is a freshly allocated page and a
      memcg context to charge.
      
      v2: prevent double charges on pre-allocated hugepages in khugepaged
      
      [hannes@cmpxchg.org: Fix crash - *hpage could be ERR_PTR instead of NULL]
        Link: http://lkml.kernel.org/r/20200512215813.GA487759@cmpxchg.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Cc: Qian Cai <cai@lca.pw>
      Link: http://lkml.kernel.org/r/20200508183105.225460-13-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      9d82c694
    • Johannes Weiner's avatar
      mm: memcontrol: switch to native NR_ANON_THPS counter · 468c3982
      Johannes Weiner authored
      With rmap memcg locking already in place for NR_ANON_MAPPED, it's just a
      small step to remove the MEMCG_RSS_HUGE wart and switch memcg to the
      native NR_ANON_THPS accounting sites.
      
      [hannes@cmpxchg.org: fixes]
        Link: http://lkml.kernel.org/r/20200512121750.GA397968@cmpxchg.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Tested-by: default avatarNaresh Kamboju <naresh.kamboju@linaro.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Acked-by: Randy Dunlap <rdunlap@infradead.org>	[build-tested]
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-12-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      468c3982
    • Johannes Weiner's avatar
      mm: memcontrol: switch to native NR_ANON_MAPPED counter · be5d0a74
      Johannes Weiner authored
      Memcg maintains a private MEMCG_RSS counter.  This divergence from the
      generic VM accounting means unnecessary code overhead, and creates a
      dependency for memcg that page->mapping is set up at the time of charging,
      so that page types can be told apart.
      
      Convert the generic accounting sites to mod_lruvec_page_state and friends
      to maintain the per-cgroup vmstat counter of NR_ANON_MAPPED.  We use
      lock_page_memcg() to stabilize page->mem_cgroup during rmap changes, the
      same way we do for NR_FILE_MAPPED.
      
      With the previous patch removing MEMCG_CACHE and the private NR_SHMEM
      counter, this patch finally eliminates the need to have page->mapping set
      up at charge time.  However, we need to have page->mem_cgroup set up by
      the time rmap runs and does the accounting, so switch the commit and the
      rmap callbacks around.
      
      v2: fix temporary accounting bug by switching rmap<->commit (Joonsoo)
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-11-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      be5d0a74
    • Johannes Weiner's avatar
      mm: memcontrol: switch to native NR_FILE_PAGES and NR_SHMEM counters · 0d1c2072
      Johannes Weiner authored
      Memcg maintains private MEMCG_CACHE and NR_SHMEM counters.  This
      divergence from the generic VM accounting means unnecessary code overhead,
      and creates a dependency for memcg that page->mapping is set up at the
      time of charging, so that page types can be told apart.
      
      Convert the generic accounting sites to mod_lruvec_page_state and friends
      to maintain the per-cgroup vmstat counters of NR_FILE_PAGES and NR_SHMEM.
      The page is already locked in these places, so page->mem_cgroup is stable;
      we only need minimal tweaks of two mem_cgroup_migrate() calls to ensure
      it's set up in time.
      
      Then replace MEMCG_CACHE with NR_FILE_PAGES and delete the private
      NR_SHMEM accounting sites.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-10-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      0d1c2072
    • Johannes Weiner's avatar
      mm: memcontrol: prepare cgroup vmstat infrastructure for native anon counters · 9da7b521
      Johannes Weiner authored
      Anonymous compound pages can be mapped by ptes, which means that if we
      want to track NR_MAPPED_ANON, NR_ANON_THPS on a per-cgroup basis, we have
      to be prepared to see tail pages in our accounting functions.
      
      Make mod_lruvec_page_state() and lock_page_memcg() deal with tail pages
      correctly, namely by redirecting to the head page which has the
      page->mem_cgroup set up.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-9-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      9da7b521
    • Johannes Weiner's avatar
      mm: memcontrol: prepare move_account for removal of private page type counters · 49e50d27
      Johannes Weiner authored
      When memcg uses the generic vmstat counters, it doesn't need to do
      anything at charging and uncharging time.  It does, however, need to
      migrate counts when pages move to a different cgroup in move_account.
      
      Prepare the move_account function for the arrival of NR_FILE_PAGES,
      NR_ANON_MAPPED, NR_ANON_THPS etc.  by having a branch for files and a
      branch for anon, which can then divided into sub-branches.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-8-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      49e50d27
    • Johannes Weiner's avatar
      mm: memcontrol: prepare uncharging for removal of private page type counters · 9f762dbe
      Johannes Weiner authored
      The uncharge batching code adds up the anon, file, kmem counts to
      determine the total number of pages to uncharge and references to drop.
      But the next patches will remove the anon and file counters.
      
      Maintain an aggregate nr_pages in the uncharge_gather struct.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-7-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      9f762dbe
    • Johannes Weiner's avatar
      mm: memcontrol: convert page cache to a new mem_cgroup_charge() API · 3fea5a49
      Johannes Weiner authored
      The try/commit/cancel protocol that memcg uses dates back to when pages
      used to be uncharged upon removal from the page cache, and thus couldn't
      be committed before the insertion had succeeded.  Nowadays, pages are
      uncharged when they are physically freed; it doesn't matter whether the
      insertion was successful or not.  For the page cache, the transaction
      dance has become unnecessary.
      
      Introduce a mem_cgroup_charge() function that simply charges a newly
      allocated page to a cgroup and sets up page->mem_cgroup in one single
      step.  If the insertion fails, the caller doesn't have to do anything but
      free/put the page.
      
      Then switch the page cache over to this new API.
      
      Subsequent patches will also convert anon pages, but it needs a bit more
      prep work.  Right now, memcg depends on page->mapping being already set up
      at the time of charging, so that it can maintain its own MEMCG_CACHE and
      MEMCG_RSS counters.  For anon, page->mapping is set under the same pte
      lock under which the page is publishd, so a single charge point that can
      block doesn't work there just yet.
      
      The following prep patches will replace the private memcg counters with
      the generic vmstat counters, thus removing the page->mapping dependency,
      then complete the transition to the new single-point charge API and delete
      the old transactional scheme.
      
      v2: leave shmem swapcache when charging fails to avoid double IO (Joonsoo)
      v3: rebase on preceeding shmem simplification patch
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-6-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      3fea5a49
    • Johannes Weiner's avatar
      mm: memcontrol: move out cgroup swaprate throttling · 6caa6a07
      Johannes Weiner authored
      The cgroup swaprate throttling is about matching new anon allocations to
      the rate of available IO when that is being throttled.  It's the io
      controller hooking into the VM, rather than a memory controller thing.
      
      Rename mem_cgroup_throttle_swaprate() to cgroup_throttle_swaprate(), and
      drop the @memcg argument which is only used to check whether the preceding
      page charge has succeeded and the fault is proceeding.
      
      We could decouple the call from mem_cgroup_try_charge() here as well, but
      that would cause unnecessary churn: the following patches convert all
      callsites to a new charge API and we'll decouple as we go along.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
      Reviewed-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
      Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200508183105.225460-5-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      6caa6a07
    • Johannes Weiner's avatar
      mm: shmem: remove rare optimization when swapin races with hole punching · 14235ab3
      Johannes Weiner authored
      Commit 215c02bc ("tmpfs: fix shmem_getpage_gfp() VM_BUG_ON")
      recognized that hole punching can race with swapin and removed the
      BUG_ON() for a truncated entry from the swapin path.
      
      The patch also added a swapcache deletion to optimize this rare case:
      Since swapin has the page locked, and free_swap_and_cache() merely
      trylocks, this situation can leave the page stranded in swapcache.
      Usually, page reclaim picks up stale swapcache pages, and the race can
      happen at any other time when the page is locked.  (The same happens for
      non-shmem swapin racing with page table zapping.) The thinking here was:
      we already observed the race and we have the page locked, we may as well
      do the cleanup instead of waiting for reclaim.
      
      However, this optimization complicates the next patch which moves the
      cgroup charging code around.  As this is just a minor speedup for a race
      condition that is so rare that it required a fuzzer to trigger the
      original BUG_ON(), it's no longer worth the complications.
      Suggested-by: default avatarHugh Dickins <hughd@google.com>
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Acked-by: default avatarHugh Dickins <hughd@google.com>
      Cc: Alex Shi <alex.shi@linux.alibaba.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Shakeel Butt <shakeelb@google.com>
      Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Roman Gushchin <guro@fb.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Link: http://lkml.kernel.org/r/20200511181056.GA339505@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      14235ab3