Messages in this thread | | | Subject | Re: [PATCH 09/14] mm: use compaction feedback for thp backoff conditions | From | Vlastimil Babka <> | Date | Thu, 28 Apr 2016 10:53:18 +0200 |
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On 04/20/2016 09:47 PM, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > > THP requests skip the direct reclaim if the compaction is either > deferred or contended to reduce stalls which wouldn't help the > allocation success anyway. These checks are ignoring other potential > feedback modes which we have available now. > > It clearly doesn't make much sense to go and reclaim few pages if the > previous compaction has failed. > > We can also simplify the check by using compaction_withdrawn which > checks for both COMPACT_CONTENDED and COMPACT_DEFERRED. This check > is however covering more reasons why the compaction was withdrawn. > None of them should be a problem for the THP case though. > > It is safe to back of if we see COMPACT_SKIPPED because that means > that compaction_suitable failed and a single round of the reclaim is > unlikely to make any difference here. We would have to be close to > the low watermark to reclaim enough and even then there is no guarantee > that the compaction would make any progress while the direct reclaim > would have caused the stall. > > COMPACT_PARTIAL_SKIPPED is slightly different because that means that we > have only seen a part of the zone so a retry would make some sense. But > it would be a compaction retry not a reclaim retry to perform. We are > not doing that and that might indeed lead to situations where THP fails > but this should happen only rarely and it would be really hard to > measure. > > Signed-off-by: Michal Hocko <mhocko@suse.com>
THP's don't compact by default in page fault path anymore, so we don't need to restrict them even more. And hopefully we'll replace the is_thp_gfp_mask() hack with something better soon, so this might be just extra code churn. But I don't feel strongly enough to nack it.
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