Messages in this thread | | | Date | Wed, 1 Jun 2016 01:56:26 +0200 | From | Oleg Nesterov <> | Subject | Re: zone_reclaimable() leads to livelock in __alloc_pages_slowpath() |
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On 05/31, Michal Hocko wrote: > > On Sun 29-05-16 23:25:40, Oleg Nesterov wrote: > > > > This single change in get_scan_count() under for_each_evictable_lru() loop > > > > - size = lruvec_lru_size(lruvec, lru); > > + size = zone_page_state_snapshot(lruvec_zone(lruvec), NR_LRU_BASE + lru); > > > > fixes the problem too. > > > > Without this change shrink*() continues to scan the LRU_ACTIVE_FILE list > > while it is empty. LRU_INACTIVE_FILE is not empty (just a few pages) but > > we do not even try to scan it, lruvec_lru_size() returns zero. > > OK, you seem to be really seeing a different issue than me.
quite possibly, but
> My debugging > patch was showing when nothing was really isolated from the LRU lists > (both for shrink_{in}active_list.
in my debugging session too. LRU_ACTIVE_FILE was empty, so there is nothing to isolate even if shrink_active_list() is (wrongly called) with nr_to_scan != 0. LRU_INACTIVE_FILE is not empty but it is not scanned because nr_to_scan == 0.
But I am afraid I misunderstood you, and you meant something else.
> > Then later we recheck zone_reclaimable() and it notices the INACTIVE_FILE > > counter because it uses the _snapshot variant, this leads to livelock. > > > > I guess this doesn't really matter, but in my particular case these > > ACTIVE/INACTIVE counters were screwed by the recent putback_inactive_pages() > > logic. The pages we "leak" in INACTIVE list were recently moved from ACTIVE > > to INACTIVE list, and this updated only the per-cpu ->vm_stat_diff[] counters, > > so the "non snapshot" lruvec_lru_size() in get_scan_count() sees the "old" > > numbers. > > Hmm. I am not really sure we can use the _snapshot version in lruvec_lru_size.
Yes, yes, I understand,
> But I am thinking whether we should simply revert 0db2cb8da89d ("mm, > vmscan: make zone_reclaimable_pages more precise") in 4.6 stable tree. > Does that help as well?
I'll test this tomorrow, but even if it helps I am not sure... Yes, this way zone_reclaimable() and get_scan_count() will see the same numbers, but how this can help to make zone_reclaimable() == F at the end?
Again, suppose that (say) ACTIVE list is empty but zone->vm_stat != 0 because there is something in per-cpu counter (so that _snapshot == 0). This means that we sill continue to try to scan this list for no reason.
But Michal, let me repeat that I do not understand this code, so I can be easily wrong.
Oleg.
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