Messages in this thread | | | Date | Fri, 16 Jan 2015 10:40:01 +0530 | From | Vinayak Menon <> | Subject | Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated |
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On 01/16/2015 06:47 AM, Andrew Morton wrote: > On Wed, 14 Jan 2015 17:06:59 +0530 Vinayak Menon <vinmenon@codeaurora.org> wrote: > >> It is observed that sometimes multiple tasks get blocked for long >> in the congestion_wait loop below, in shrink_inactive_list. This >> is because of vm_stat values not being synced. >> >> (__schedule) from [<c0a03328>] >> (schedule_timeout) from [<c0a04940>] >> (io_schedule_timeout) from [<c01d585c>] >> (congestion_wait) from [<c01cc9d8>] >> (shrink_inactive_list) from [<c01cd034>] >> (shrink_zone) from [<c01cdd08>] >> (try_to_free_pages) from [<c01c442c>] >> (__alloc_pages_nodemask) from [<c01f1884>] >> (new_slab) from [<c09fcf60>] >> (__slab_alloc) from [<c01f1a6c>] >> >> In one such instance, zone_page_state(zone, NR_ISOLATED_FILE) >> had returned 14, zone_page_state(zone, NR_INACTIVE_FILE) >> returned 92, and GFP_IOFS was set, and this resulted >> in too_many_isolated returning true. But one of the CPU's >> pageset vm_stat_diff had NR_ISOLATED_FILE as "-14". So the >> actual isolated count was zero. As there weren't any more >> updates to NR_ISOLATED_FILE and vmstat_update deffered work >> had not been scheduled yet, 7 tasks were spinning in the >> congestion wait loop for around 4 seconds, in the direct >> reclaim path. >> >> This patch uses zone_page_state_snapshot instead, but restricts >> its usage to avoid performance penalty. > > Seems reasonable. > >> >> ... >> >> @@ -1516,15 +1531,18 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, >> unsigned long nr_immediate = 0; >> isolate_mode_t isolate_mode = 0; >> int file = is_file_lru(lru); >> + int safe = 0; >> struct zone *zone = lruvec_zone(lruvec); >> struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; >> >> - while (unlikely(too_many_isolated(zone, file, sc))) { >> + while (unlikely(too_many_isolated(zone, file, sc, safe))) { >> congestion_wait(BLK_RW_ASYNC, HZ/10); >> >> /* We are about to die and free our memory. Return now. */ >> if (fatal_signal_pending(current)) >> return SWAP_CLUSTER_MAX; >> + >> + safe = 1; >> } > > But here and under the circumstances you describe, we'll call > congestion_wait() a single time. That shouldn't have occurred. > > So how about we put the fallback logic into too_many_isolated() itself? > >
congestion_wait was allowed to run once as an optimization, considering that __too_many_isolated (unsafe and faster) can be correct in returning true most of the time. So we avoid calling the safe version, in most of the cases. But I agree that we should not call congestion_wait unnecessarily even in those rare cases. So this looks correct to me.
> > From: Andrew Morton <akpm@linux-foundation.org> > Subject: mm-vmscan-fix-the-page-state-calculation-in-too_many_isolated-fix > > Move the zone_page_state_snapshot() fallback logic into > too_many_isolated(), so shrink_inactive_list() doesn't incorrectly call > congestion_wait(). > > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Michal Hocko <mhocko@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Vinayak Menon <vinmenon@codeaurora.org> > Cc: Vladimir Davydov <vdavydov@parallels.com> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > mm/vmscan.c | 23 +++++++++++------------ > 1 file changed, 11 insertions(+), 12 deletions(-) > > diff -puN mm/vmscan.c~mm-vmscan-fix-the-page-state-calculation-in-too_many_isolated-fix mm/vmscan.c > --- a/mm/vmscan.c~mm-vmscan-fix-the-page-state-calculation-in-too_many_isolated-fix > +++ a/mm/vmscan.c > @@ -1402,7 +1402,7 @@ int isolate_lru_page(struct page *page) > } > > static int __too_many_isolated(struct zone *zone, int file, > - struct scan_control *sc, int safe) > + struct scan_control *sc, int safe) > { > unsigned long inactive, isolated; > > @@ -1435,7 +1435,7 @@ static int __too_many_isolated(struct zo > * unnecessary swapping, thrashing and OOM. > */ > static int too_many_isolated(struct zone *zone, int file, > - struct scan_control *sc, int safe) > + struct scan_control *sc) > { > if (current_is_kswapd()) > return 0; > @@ -1443,12 +1443,14 @@ static int too_many_isolated(struct zone > if (!global_reclaim(sc)) > return 0; > > - if (unlikely(__too_many_isolated(zone, file, sc, 0))) { > - if (safe) > - return __too_many_isolated(zone, file, sc, safe); > - else > - return 1; > - } > + /* > + * __too_many_isolated(safe=0) is fast but inaccurate, because it > + * doesn't account for the vm_stat_diff[] counters. So if it looks > + * like too_many_isolated() is about to return true, fall back to the > + * slower, more accurate zone_page_state_snapshot(). > + */ > + if (unlikely(__too_many_isolated(zone, file, sc, 0))) > + return __too_many_isolated(zone, file, sc, safe); > > return 0; > } > @@ -1540,18 +1542,15 @@ shrink_inactive_list(unsigned long nr_to > unsigned long nr_immediate = 0; > isolate_mode_t isolate_mode = 0; > int file = is_file_lru(lru); > - int safe = 0; > struct zone *zone = lruvec_zone(lruvec); > struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; > > - while (unlikely(too_many_isolated(zone, file, sc, safe))) { > + while (unlikely(too_many_isolated(zone, file, sc))) { > congestion_wait(BLK_RW_ASYNC, HZ/10); > > /* We are about to die and free our memory. Return now. */ > if (fatal_signal_pending(current)) > return SWAP_CLUSTER_MAX; > - > - safe = 1; > } > > lru_add_drain(); > _ >
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