On Mon 11-04-16 13:02:20, Vlastimil Babka wrote: > On 04/05/2016 01:25 PM, Michal Hocko wrote: > >From: Michal Hocko <[email protected]> > > > >try_to_compact_pages can currently return COMPACT_SKIPPED even when the > >compaction is defered for some zone just because zone DMA is skipped > >in 99% of cases due to watermark checks. This makes COMPACT_DEFERRED > >basically unusable for the page allocator as a feedback mechanism. > > > >Make sure we distinguish those two states properly and switch their > >ordering in the enum. This would mean that the COMPACT_SKIPPED will be > >returned only when all eligible zones are skipped. > > > >This shouldn't introduce any functional change. > > Hmm, really? __alloc_pages_direct_compact() does distinguish > COMPACT_DEFERRED, and sets *deferred compaction, so ultimately this is some > change for THP allocations?
Hmm, you are right. In cases where we would return COMPACTION_SKIPED even though there is a zone which would really like to tell us COMPACT_DEFERRED then we would previously did __alloc_pages_direct_reclaim and then bail out for THP which do not have __GFP_REPEAT while now we would recognize DEFERRED and bail out without the direct reclaim. So there is a functional change. Adnrew, could you drop the sentence about no functional change and replace it by the following? " As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath will be more precise and we would bail out rather than reclaim. " > Also there's no mention of COMPACT_INACTIVE in the changelog (which indeed > isn't functional change, but might surprise somebody). > > >Signed-off-by: Michal Hocko <[email protected]> > > Patch itself is OK. > > Acked-by: Vlastimil Babka <[email protected]> Thanks! -- Michal Hocko SUSE Labs
