• Hugh Dickins's avatar
    mm: stop leaking PageTables · b0b9b3df
    Hugh Dickins authored
    4.10-rc loadtest (even on x86, and even without THPCache) fails with
    "fork: Cannot allocate memory" or some such; and /proc/meminfo shows
    PageTables growing.
    
    Commit 953c66c2 ("mm: THP page cache support for ppc64") that got
    merged in rc1 removed the freeing of an unused preallocated pagetable
    after do_fault_around() has called map_pages().
    
    This is usually a good optimization, so that the followup doesn't have
    to reallocate one; but it's not sufficient to shift the freeing into
    alloc_set_pte(), since there are failure cases (most commonly
    VM_FAULT_RETRY) which never reach finish_fault().
    
    Check and free it at the outer level in do_fault(), then we don't need
    to worry in alloc_set_pte(), and can restore that to how it was (I
    cannot find any reason to pte_free() under lock as it was doing).
    
    And fix a separate pagetable leak, or crash, introduced by the same
    change, that could only show up on some ppc64: why does do_set_pmd()'s
    failure case attempt to withdraw a pagetable when it never deposited
    one, at the same time overwriting (so leaking) the vmf->prealloc_pte?
    Residue of an earlier implementation, perhaps? Delete it.
    
    Fixes: 953c66c2 ("mm: THP page cache support for ppc64")
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Michael Neuling <mikey@neuling.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Balbir Singh <bsingharora@gmail.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    b0b9b3df
memory.c 112 KB