• Vladimir Davydov's avatar
    mm: workingset: size shadow nodes lru basing on file cache size · cdcbb72e
    Vladimir Davydov authored
    A page is activated on refault if the refault distance stored in the
    corresponding shadow entry is less than the number of active file pages.
    Since active file pages can't occupy more than half memory, we assume
    that the maximal effective refault distance can't be greater than half
    the number of present pages and size the shadow nodes lru list
    appropriately.  Generally speaking, this assumption is correct, but it
    can result in wasting a considerable chunk of memory on stale shadow
    nodes in case the portion of file pages is small, e.g.  if a workload
    mostly uses anonymous memory.
    
    To sort this out, we need to compute the size of shadow nodes lru basing
    not on the maximal possible, but the current size of file cache.  We
    could take the size of active file lru for the maximal refault distance,
    but active lru is pretty unstable - it can shrink dramatically at
    runtime possibly disrupting workingset detection logic.
    
    Instead we assume that the maximal refault distance equals half the
    total number of file cache pages.  This will protect us against active
    file lru size fluctuations while still being correct, because size of
    active lru is normally maintained lower than size of inactive lru.
    Signed-off-by: default avatarVladimir Davydov <vdavydov@virtuozzo.com>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cdcbb72e
workingset.c 16.8 KB