Messages in this thread | | | Date | Tue, 26 Jul 2016 10:21:57 +0900 | From | Minchan Kim <> | Subject | Re: [RFC] mm: bail out in shrin_inactive_list |
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On Mon, Jul 25, 2016 at 10:29:09AM +0100, Mel Gorman wrote: > There is a typo in the subject line. > > 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. > > Rephease -- The problem is that if the inactive list is full of highmem > pages then a direct reclaimer searching for a lowmem page waste CPU > scanning uselessly.
It's better. Thanks.
> > > 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@kernel.org> > > --- > > 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? > > > > I think it's ok to ignore memcg in this case as a memcg shrink is often > going to be for pages that can use highmem anyway.
So, you mean it's okay to ignore kmemcg case? If memcg guys agree it, I want to make get_scan_count consider reclaimable lru size under the reclaim constraint, instead.
> > > mm/vmscan.c | 28 ++++++++++++++++++++++++++++ > > 1 file changed, 28 insertions(+) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index e5af357..3d285cc 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1652,6 +1652,31 @@ static int current_may_throttle(void) > > bdi_write_congested(current->backing_dev_info); > > } > > > > +static inline bool inactive_reclaimable_pages(struct lruvec *lruvec, > > + struct scan_control *sc, > > + enum lru_list lru) > > inline is unnecessary. The function is long but only has one caller so > it'll be inlined automatically. > > > +{ > > + int zid; > > + struct zone *zone; > > + bool file = is_file_lru(lru); > > It's more appropriate to use int for file in this case as it's used as a > multiplier. It'll work either way. > > Otherwise; > > Acked-by: Mel Gorman <mgorman@techsingularity.net> > > -- > Mel Gorman > SUSE Labs
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