• Hugh Dickins's avatar
    memcgroup: revert swap_state mods · fa1de900
    Hugh Dickins authored
    If we're charging rss and we're charging cache, it seems obvious that we
    should be charging swapcache - as has been done.  But in practice that
    doesn't work out so well: both swapin readahead and swapoff leave the
    majority of pages charged to the wrong cgroup (the cgroup that happened to
    read them in, rather than the cgroup to which they belong).
    
    (Which is why unuse_pte's GFP_KERNEL while holding pte lock never showed up
    as a problem: no allocation was ever done there, every page read being
    already charged to the cgroup which initiated the swapoff.)
    
    It all works rather better if we leave the charging to do_swap_page and
    unuse_pte, and do nothing for swapcache itself: revert mm/swap_state.c to
    what it was before the memory-controller patches.  This also speeds up
    significantly a contained process working at its limit: because it no
    longer needs to keep waiting for swap writeback to complete.
    
    Is it unfair that swap pages become uncharged once they're unmapped, even
    though they're still clearly private to particular cgroups?  For a short
    while, yes; but PageReclaim arranges for those pages to go to the end of
    the inactive list and be reclaimed soon if necessary.
    
    shmem/tmpfs pages are a distinct case: their charging also benefits from
    this change, but their second life on the lists as swapcache pages may
    prove more unfair - that I need to check next.
    Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
    Cc: Pavel Emelianov <xemul@openvz.org>
    Acked-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
    Cc: Paul Menage <menage@google.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Kirill Korotaev <dev@sw.ru>
    Cc: Herbert Poetzl <herbert@13thfloor.at>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fa1de900
swap_state.c 9.66 KB