Messages in this thread | | | Date | Tue, 29 Jul 2014 11:02:08 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCH v5 02/14] mm, compaction: defer each zone individually instead of preferred zone |
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On 07/29/2014 01:59 AM, David Rientjes wrote: >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1122,28 +1122,27 @@ int sysctl_extfrag_threshold = 500; >> * @nodemask: The allowed nodes to allocate from >> * @mode: The migration mode for async, sync light, or sync migration >> * @contended: Return value that is true if compaction was aborted due to lock contention >> - * @page: Optionally capture a free page of the requested order during compaction > > Never noticed this non-existant formal before.
It's a leftover from the first Mel's page capture attempt that was partially reverted.
>> + * @candidate_zone: Return the zone where we think allocation should succeed >> * >> * This is the main entry point for direct page compaction. >> */ >> unsigned long try_to_compact_pages(struct zonelist *zonelist, >> int order, gfp_t gfp_mask, nodemask_t *nodemask, >> - enum migrate_mode mode, bool *contended) >> + enum migrate_mode mode, bool *contended, >> + struct zone **candidate_zone) >> { >> enum zone_type high_zoneidx = gfp_zone(gfp_mask); >> int may_enter_fs = gfp_mask & __GFP_FS; >> int may_perform_io = gfp_mask & __GFP_IO; >> struct zoneref *z; >> struct zone *zone; >> - int rc = COMPACT_SKIPPED; >> + int rc = COMPACT_DEFERRED; >> int alloc_flags = 0; >> >> /* Check if the GFP flags allow compaction */ >> if (!order || !may_enter_fs || !may_perform_io) >> return rc; >> > > It doesn't seem right that if we called try_to_compact_pages() in a > context where it is useless (order-0 or non-GFP_KERNEL allocation) that we > would return COMPACT_DEFERRED. I think the existing semantics before the > patch, that is > > - deferred: compaction was tried but failed, so avoid subsequent calls in > the near future that may be potentially expensive, and > > - skipped: compaction wasn't tried because it will be useless > > is correct and deferred shouldn't take on another meaning, which now will > set deferred_compaction == true in the page allocator. It probably > doesn't matter right now because the only check of deferred_compaction is > effective for __GFP_NO_KSWAPD, i.e. it is both high-order and GFP_KERNEL, > but it seems returning COMPACT_SKIPPED here would also work fine and be > more appropriate.
You're right. That was an oversight, not intention. Thanks for catching that.
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