4.4-stable review patch. If anyone has any objections, please let me know.
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From: Vladimir Davydov vdavydov@virtuozzo.com
commit 316bda0e6cc5f36f94b4af8bded16d642c90ad75 upstream.
We assume there is enough inactive page cache if the size of inactive file lru is greater than the size of active file lru, in which case we force-scan file lru ignoring anonymous pages. While this logic works fine when there are plenty of page cache pages, it fails if the size of file lru is small (several MB): in this case (lru_size >> prio) will be 0 for normal scan priorities, as a result, if inactive file lru happens to be larger than active file lru, anonymous pages of a cgroup will never get evicted unless the system experiences severe memory pressure, even if there are gigabytes of unused anonymous memory there, which is unfair in respect to other cgroups, whose workloads might be page cache oriented.
This patch attempts to fix this by elaborating the "enough inactive page cache" check: it makes it not only check that inactive lru size > active lru size, but also that we will scan something from the cgroup at the current scan priority. If these conditions do not hold, we proceed to SCAN_FRACT as usual.
Signed-off-by: Vladimir Davydov vdavydov@virtuozzo.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Mel Gorman mgorman@techsingularity.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Mel Gorman mgorman@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/vmscan.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2057,10 +2057,16 @@ static void get_scan_count(struct lruvec }
/* - * There is enough inactive page cache, do not reclaim - * anything from the anonymous working set right now. + * If there is enough inactive page cache, i.e. if the size of the + * inactive list is greater than that of the active list *and* the + * inactive list actually has some pages to scan on this priority, we + * do not reclaim anything from the anonymous working set right now. + * Without the second condition we could end up never scanning an + * lruvec even if it has plenty of old anonymous pages unless the + * system is under heavy pressure. */ - if (!inactive_file_is_low(lruvec)) { + if (!inactive_file_is_low(lruvec) && + get_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) { scan_balance = SCAN_FILE; goto out; }