On Fri, Jul 29, 2016 at 10:11:30AM -0400, Johannes Weiner wrote: > On Mon, Jul 25, 2016 at 04:51:59PM +0900, Minchan Kim wrote: > > With node-lru, if there are enough reclaimable pages in highmem > > but nothing in lowmem, VM can try to shrink inactive list although > > the requested zone is lowmem. > > > > The problem is direct reclaimer scans inactive list is fulled with > > highmem pages to find a victim page at a reqested zone or lower zones > > but the result is that VM should skip all of pages. It just burns out > > CPU. Even, many direct reclaimers are stalled by too_many_isolated > > if lots of parallel reclaimer are going on although there are no > > reclaimable memory in inactive list. > > > > I tried the experiment 4 times in 32bit 2G 8 CPU KVM machine > > to get elapsed time. > > > > hackbench 500 process 2 > > > > = Old = > > > > 1st: 289s 2nd: 310s 3rd: 112s 4th: 272s > > > > = Now = > > > > 1st: 31s 2nd: 132s 3rd: 162s 4th: 50s. > > > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > --- > > I believe proper fix is to modify get_scan_count. IOW, I think > > we should introduce lruvec_reclaimable_lru_size with proper > > classzone_idx but I don't know how we can fix it with memcg > > which doesn't have zone stat now. should introduce zone stat > > back to memcg? Or, it's okay to ignore memcg? > > You can fully ignore memcg and kmemcg. They only care about the > balance sheet - page in, page out - never mind the type of page. > > If you are allocating a slab object and there is no physical memory, > you'll wake kswapd or enter direct reclaim with the restricted zone > index. If you then try to charge the freshly allocated page or object > but hit the limit, kmem or otherwise, you'll enter memcg reclaim that > is not restricted and only cares about getting usage + pages < limit. Thanks. I got understood. > > I agree that it might be better to put this logic in get_scan_count() > and set both nr[lru] as well as *lru_pages according to the pages that > are eligible for the given reclaim index. > > if (global_reclaim(sc)) > add zone stats from 0 to sc->reclaim_idx > else > use lruvec_lru_size() Yeb, I already sent it. http://lkml.kernel.org/r/1469604588-6051-2-git-send-email-minchan@xxxxxxxxxx Thanks for the review, Johannes! > > It's a bit unfortunate that abstractions like the lruvec fall apart > when we have to reconstruct zones ad-hoc now, but I don't see any > obvious way around it... -- 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>