On Mon 23-11-15 13:39:33, Vladimir Davydov wrote: > 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. Yes this makes sense. FWIW I have a similar patch waiting for feedback from testing which catches the other extreme case when we force anon pages scan without any progress from the kswapd context (I hope I get to post it soon). get_scan_count is getting more and more convoluted :/ > Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > --- > Changes in v2: > - remove unnecessary > 0 (Johannes) > - elaborate on the comment (Andrew) > > mm/vmscan.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bd2918e6391a..97ba9e1cde09 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2043,10 +2043,16 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness, > } > > /* > - * 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; > } > -- > 2.1.4 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>