On 04/11/2016 08:45 AM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx>
while playing with the oom detection rework [1] I have noticed
that my heavy order-9 (hugetlb) load close to OOM ended up in an
endless loop where the reclaim hasn't made any progress but
did_some_progress didn't reflect that and compaction_suitable
was backing off because no zone is above low wmark + 1 << order.
It turned out that this is in fact an old standing bug in compaction_ready
which ignores the requested_highidx and did the watermark check for
0 classzone_idx. This succeeds for zone DMA most of the time as the zone
is mostly unused because of lowmem protection. This also means that the
OOM killer wouldn't be triggered for higher order requests even when
there is no reclaim progress and we essentially rely on order-0 request
to find this out. This has been broken in one way or another since
fe4b1b244bdb ("mm: vmscan: when reclaiming for compaction, ensure there
are sufficient free pages available") but only since 7335084d446b ("mm:
vmscan: do not OOM if aborting reclaim to start compaction") we are not
invoking the OOM killer based on the wrong calculation.
Propagate requested_highidx down to compaction_ready and use it for both
the watermak check and compaction_suitable to fix this issue.
[1] http://lkml.kernel.org/r/1459855533-4600-1-git-send-email-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
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