1. 12 Sep, 2013 6 commits
    • Michal Hocko's avatar
      memcg, vmscan: integrate soft reclaim tighter with zone shrinking code · 3b38722e
      Michal Hocko authored
      This patchset is sitting out of tree for quite some time without any
      objections.  I would be really happy if it made it into 3.12.  I do not
      want to push it too hard but I think this work is basically ready and
      waiting more doesn't help.
      
      The basic idea is quite simple.  Pull soft reclaim into shrink_zone in the
      first step and get rid of the previous soft reclaim infrastructure.
      shrink_zone is done in two passes now.  First it tries to do the soft
      limit reclaim and it falls back to reclaim-all mode if no group is over
      the limit or no pages have been scanned.  The second pass happens at the
      same priority so the only time we waste is the memcg tree walk which has
      been updated in the third step to have only negligible overhead.
      
      As a bonus we will get rid of a _lot_ of code by this and soft reclaim
      will not stand out like before when it wasn't integrated into the zone
      shrinking code and it reclaimed at priority 0 (the testing results show
      that some workloads suffers from such an aggressive reclaim).  The clean
      up is in a separate patch because I felt it would be easier to review that
      way.
      
      The second step is soft limit reclaim integration into targeted reclaim.
      It should be rather straight forward.  Soft limit has been used only for
      the global reclaim so far but it makes sense for any kind of pressure
      coming from up-the-hierarchy, including targeted reclaim.
      
      The third step (patches 4-8) addresses the tree walk overhead by enhancing
      memcg iterators to enable skipping whole subtrees and tracking number of
      over soft limit children at each level of the hierarchy.  This information
      is updated same way the old soft limit tree was updated (from
      memcg_check_events) so we shouldn't see an additional overhead.  In fact
      mem_cgroup_update_soft_limit is much simpler than tree manipulation done
      previously.
      
      __shrink_zone uses mem_cgroup_soft_reclaim_eligible as a predicate for
      mem_cgroup_iter so the decision whether a particular group should be
      visited is done at the iterator level which allows us to decide to skip
      the whole subtree as well (if there is no child in excess).  This reduces
      the tree walk overhead considerably.
      
      * TEST 1
      ========
      
      My primary test case was a parallel kernel build with 2 groups (make is
      running with -j8 with a distribution .config in a separate cgroup without
      any hard limit) on a 32 CPU machine booted with 1GB memory and both builds
      run taskset to Node 0 cpus.
      
      I was mostly interested in 2 setups.  Default - no soft limit set and -
      and 0 soft limit set to both groups.  The first one should tell us whether
      the rework regresses the default behavior while the second one should show
      us improvements in an extreme case where both workloads are always over
      the soft limit.
      
      /usr/bin/time -v has been used to collect the statistics and each
      configuration had 3 runs after fresh boot without any other load on the
      system.
      
      base is mmotm-2013-07-18-16-40
      rework all 8 patches applied on top of base
      
      * No-limit
      User
      no-limit/base: min: 651.92 max: 672.65 avg: 664.33 std: 8.01 runs: 6
      no-limit/rework: min: 657.34 [100.8%] max: 668.39 [99.4%] avg: 663.13 [99.8%] std: 3.61 runs: 6
      System
      no-limit/base: min: 69.33 max: 71.39 avg: 70.32 std: 0.79 runs: 6
      no-limit/rework: min: 69.12 [99.7%] max: 71.05 [99.5%] avg: 70.04 [99.6%] std: 0.59 runs: 6
      Elapsed
      no-limit/base: min: 398.27 max: 422.36 avg: 408.85 std: 7.74 runs: 6
      no-limit/rework: min: 386.36 [97.0%] max: 438.40 [103.8%] avg: 416.34 [101.8%] std: 18.85 runs: 6
      
      The results are within noise. Elapsed time has a bigger variance but the
      average looks good.
      
      * 0-limit
      User
      0-limit/base: min: 573.76 max: 605.63 avg: 585.73 std: 12.21 runs: 6
      0-limit/rework: min: 645.77 [112.6%] max: 666.25 [110.0%] avg: 656.97 [112.2%] std: 7.77 runs: 6
      System
      0-limit/base: min: 69.57 max: 71.13 avg: 70.29 std: 0.54 runs: 6
      0-limit/rework: min: 68.68 [98.7%] max: 71.40 [100.4%] avg: 69.91 [99.5%] std: 0.87 runs: 6
      Elapsed
      0-limit/base: min: 1306.14 max: 1550.17 avg: 1430.35 std: 90.86 runs: 6
      0-limit/rework: min: 404.06 [30.9%] max: 465.94 [30.1%] avg: 434.81 [30.4%] std: 22.68 runs: 6
      
      The improvement is really huge here (even bigger than with my previous
      testing and I suspect that this highly depends on the storage).  Page
      fault statistics tell us at least part of the story:
      
      Minor
      0-limit/base: min: 37180461.00 max: 37319986.00 avg: 37247470.00 std: 54772.71 runs: 6
      0-limit/rework: min: 36751685.00 [98.8%] max: 36805379.00 [98.6%] avg: 36774506.33 [98.7%] std: 17109.03 runs: 6
      Major
      0-limit/base: min: 170604.00 max: 221141.00 avg: 196081.83 std: 18217.01 runs: 6
      0-limit/rework: min: 2864.00 [1.7%] max: 10029.00 [4.5%] avg: 5627.33 [2.9%] std: 2252.71 runs: 6
      
      Same as with my previous testing Minor faults are more or less within
      noise but Major fault count is way bellow the base kernel.
      
      While this looks as a nice win it is fair to say that 0-limit
      configuration is quite artificial. So I was playing with 0-no-limit
      loads as well.
      
      * TEST 2
      ========
      
      The following results are from 2 groups configuration on a 16GB machine
      (single NUMA node).
      
      - A running stream IO (dd if=/dev/zero of=local.file bs=1024) with
        2*TotalMem with 0 soft limit.
      - B running a mem_eater which consumes TotalMem-1G without any limit. The
        mem_eater consumes the memory in 100 chunks with 1s nap after each
        mmap+poppulate so that both loads have chance to fight for the memory.
      
      The expected result is that B shouldn't be reclaimed and A shouldn't see
      a big dropdown in elapsed time.
      
      User
      base: min: 2.68 max: 2.89 avg: 2.76 std: 0.09 runs: 3
      rework: min: 3.27 [122.0%] max: 3.74 [129.4%] avg: 3.44 [124.6%] std: 0.21 runs: 3
      System
      base: min: 86.26 max: 88.29 avg: 87.28 std: 0.83 runs: 3
      rework: min: 81.05 [94.0%] max: 84.96 [96.2%] avg: 83.14 [95.3%] std: 1.61 runs: 3
      Elapsed
      base: min: 317.28 max: 332.39 avg: 325.84 std: 6.33 runs: 3
      rework: min: 281.53 [88.7%] max: 298.16 [89.7%] avg: 290.99 [89.3%] std: 6.98 runs: 3
      
      System time improved slightly as well as Elapsed. My previous testing
      has shown worse numbers but this again seem to depend on the storage
      speed.
      
      My theory is that the writeback doesn't catch up and prio-0 soft reclaim
      falls into wait on writeback page too often in the base kernel. The
      patched kernel doesn't do that because the soft reclaim is done from the
      kswapd/direct reclaim context. This can be seen on the following graph
      nicely. The A's group usage_in_bytes regurarly drops really low very often.
      
      All 3 runs
      http://labs.suse.cz/mhocko/soft_limit_rework/stream_io-vs-mem_eater/stream.png
      resp. a detail of the single run
      http://labs.suse.cz/mhocko/soft_limit_rework/stream_io-vs-mem_eater/stream-one-run.png
      
      mem_eater seems to be doing better as well. It gets to the full
      allocation size faster as can be seen on the following graph:
      http://labs.suse.cz/mhocko/soft_limit_rework/stream_io-vs-mem_eater/mem_eater-one-run.png
      
      /proc/meminfo collected during the test also shows that rework kernel
      hasn't swapped that much (well almost not at all):
      base: max: 123900 K avg: 56388.29 K
      rework: max: 300 K avg: 128.68 K
      
      kswapd and direct reclaim statistics are of no use unfortunatelly because
      soft reclaim is not accounted properly as the counters are hidden by
      global_reclaim() checks in the base kernel.
      
      * TEST 3
      ========
      
      Another test was the same configuration as TEST2 except the stream IO was
      replaced by a single kbuild (16 parallel jobs bound to Node0 cpus same as
      in TEST1) and mem_eater allocated TotalMem-200M so kbuild had only 200MB
      left.
      
      Kbuild did better with the rework kernel here as well:
      User
      base: min: 860.28 max: 872.86 avg: 868.03 std: 5.54 runs: 3
      rework: min: 880.81 [102.4%] max: 887.45 [101.7%] avg: 883.56 [101.8%] std: 2.83 runs: 3
      System
      base: min: 84.35 max: 85.06 avg: 84.79 std: 0.31 runs: 3
      rework: min: 85.62 [101.5%] max: 86.09 [101.2%] avg: 85.79 [101.2%] std: 0.21 runs: 3
      Elapsed
      base: min: 135.36 max: 243.30 avg: 182.47 std: 45.12 runs: 3
      rework: min: 110.46 [81.6%] max: 116.20 [47.8%] avg: 114.15 [62.6%] std: 2.61 runs: 3
      Minor
      base: min: 36635476.00 max: 36673365.00 avg: 36654812.00 std: 15478.03 runs: 3
      rework: min: 36639301.00 [100.0%] max: 36695541.00 [100.1%] avg: 36665511.00 [100.0%] std: 23118.23 runs: 3
      Major
      base: min: 14708.00 max: 53328.00 avg: 31379.00 std: 16202.24 runs: 3
      rework: min: 302.00 [2.1%] max: 414.00 [0.8%] avg: 366.33 [1.2%] std: 47.22 runs: 3
      
      Again we can see a significant improvement in Elapsed (it also seems to
      be more stable), there is a huge dropdown for the Major page faults and
      much more swapping:
      base: max: 583736 K avg: 112547.43 K
      rework: max: 4012 K avg: 124.36 K
      
      Graphs from all three runs show the variability of the kbuild quite
      nicely.  It even seems that it took longer after every run with the base
      kernel which would be quite surprising as the source tree for the build is
      removed and caches are dropped after each run so the build operates on a
      freshly extracted sources everytime.
      http://labs.suse.cz/mhocko/soft_limit_rework/stream_io-vs-mem_eater/kbuild-mem_eater.png
      
      My other testing shows that this is just a matter of timing and other runs
      behave differently the std for Elapsed time is similar ~50.  Example of
      other three runs:
      http://labs.suse.cz/mhocko/soft_limit_rework/stream_io-vs-mem_eater/kbuild-mem_eater2.png
      
      So to wrap this up.  The series is still doing good and improves the soft
      limit.
      
      The testing results for bunch of cgroups with both stream IO and kbuild
      loads can be found in "memcg: track children in soft limit excess to
      improve soft limit".
      
      This patch:
      
      Memcg soft reclaim has been traditionally triggered from the global
      reclaim paths before calling shrink_zone.  mem_cgroup_soft_limit_reclaim
      then picked up a group which exceeds the soft limit the most and reclaimed
      it with 0 priority to reclaim at least SWAP_CLUSTER_MAX pages.
      
      The infrastructure requires per-node-zone trees which hold over-limit
      groups and keep them up-to-date (via memcg_check_events) which is not cost
      free.  Although this overhead hasn't turned out to be a bottle neck the
      implementation is suboptimal because mem_cgroup_update_tree has no idea
      which zones consumed memory over the limit so we could easily end up
      having a group on a node-zone tree having only few pages from that
      node-zone.
      
      This patch doesn't try to fix node-zone trees management because it seems
      that integrating soft reclaim into zone shrinking sounds much easier and
      more appropriate for several reasons.  First of all 0 priority reclaim was
      a crude hack which might lead to big stalls if the group's LRUs are big
      and hard to reclaim (e.g.  a lot of dirty/writeback pages).  Soft reclaim
      should be applicable also to the targeted reclaim which is awkward right
      now without additional hacks.  Last but not least the whole infrastructure
      eats quite some code.
      
      After this patch shrink_zone is done in 2 passes.  First it tries to do
      the soft reclaim if appropriate (only for global reclaim for now to keep
      compatible with the original state) and fall back to ignoring soft limit
      if no group is eligible to soft reclaim or nothing has been scanned during
      the first pass.  Only groups which are over their soft limit or any of
      their parents up the hierarchy is over the limit are considered eligible
      during the first pass.
      
      Soft limit tree which is not necessary anymore will be removed in the
      follow up patch to make this patch smaller and easier to review.
      Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
      Reviewed-by: default avatarGlauber Costa <glommer@openvz.org>
      Reviewed-by: default avatarTejun Heo <tj@kernel.org>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
      Cc: Ying Han <yinghan@google.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Michel Lespinasse <walken@google.com>
      Cc: Greg Thelen <gthelen@google.com>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Balbir Singh <bsingharora@gmail.com>
      Cc: Glauber Costa <glommer@gmail.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      3b38722e
    • Li Zefan's avatar
      memcg: remove redundant code in mem_cgroup_force_empty_write() · c33bd835
      Li Zefan authored
      vfs guarantees the cgroup won't be destroyed, so it's redundant to get a
      css reference.
      Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
      Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
      Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: Tejun Heo <tj@kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c33bd835
    • Linus Torvalds's avatar
      Bye, bye, WfW flag · d5d04bb4
      Linus Torvalds authored
      This reverts the Linux for Workgroups thing.  And no, before somebody
      asks, we're not doing Linux95.  Not for a few years, at least.
      
      Sure, the flag added some color to the logo, and could have remained as
      a testament to my leet gimp skills.  But no.  And I'll do this early, to
      avoid the chance of forgetting when I'm doing the actual rc1 release on
      the road.
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d5d04bb4
    • Linus Torvalds's avatar
      Merge tag 'ecryptfs-3.12-rc1-crypt-ctx' of... · 1ae276a9
      Linus Torvalds authored
      Merge tag 'ecryptfs-3.12-rc1-crypt-ctx' of git://git.kernel.org/pub/scm/linux/kernel/git/tyhicks/ecryptfs
      
      Pull eCryptfs fixes from Tyler Hicks:
       "Two small fixes to the code that initializes the per-file crypto
        contexts"
      
      * tag 'ecryptfs-3.12-rc1-crypt-ctx' of git://git.kernel.org/pub/scm/linux/kernel/git/tyhicks/ecryptfs:
        ecryptfs: avoid ctx initialization race
        ecryptfs: remove check for if an array is NULL
      1ae276a9
    • Linus Torvalds's avatar
      Merge branch 'for-v3.12-fix' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping · 3b38f56c
      Linus Torvalds authored
      Pull DMA-mapping fix from Marek Szyprowski:
       "A build bugfix for the device tree support for reserved memory
        regions.  Due to superfluous include the common code failed to build
        on ARM64 and MIPS architectures.
      
        The patch that caused the build break has lived at linux-next for
        about two weeks and noone noticed the issue, what convinced me that
        everything was ok"
      
      * 'for-v3.12-fix' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping:
        drivers: of: fix build break if asm/dma-contiguous.h is missing
      3b38f56c
    • Linus Torvalds's avatar
      Merge tag 'for-3.12' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf · b3b75684
      Linus Torvalds authored
      Pull dma-buf updates from Sumit Semwal:
       "Yet another small one - dma-buf framework now supports size discovery
        of the buffer via llseek"
      
      * tag 'for-3.12' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf:
        dma-buf: Expose buffer size to userspace (v2)
        dma-buf: Check return value of anon_inode_getfile
      b3b75684
  2. 11 Sep, 2013 34 commits