The vmstat interfaces are good at hiding negative counts (at least
when CONFIG_SMP); but if you peer behind the curtain, you find that
nr_isolated_anon and nr_isolated_file soon go negative, and grow ever
more negative: so they can absorb larger and larger numbers of isolated
pages, yet still appear to be zero.
I'm happy to avoid a congestion_wait() when too_many_isolated() myself;
but I guess it's there for a good reason, in which case we ought to get
too_many_isolated() working again.
The imbalance comes from isolate_migratepages()'s ISOLATE_ABORT case:
putback_movable_pages() decrements the NR_ISOLATED counts, but we forgot
to call acct_isolated() to increment them.
Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v3.18+
---
mm/compaction.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- v3.19/mm/compaction.c 2015-02-08 18:54:22.000000000 -0800
+++ linux/mm/compaction.c 2015-02-10 22:25:04.613907871 -0800
@@ -1015,8 +1015,10 @@ static isolate_migrate_t isolate_migrate
low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
isolate_mode);
- if (!low_pfn || cc->contended)
+ if (!low_pfn || cc->contended) {
+ acct_isolated(zone, cc);
return ISOLATE_ABORT;
+ }
/*
* Either we isolated something and proceed with migration. Or
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