Messages in this thread | | | Date | Thu, 07 Aug 2014 10:53:01 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCH v2 5/8] mm/isolation: change pageblock isolation logic to fix freepage counting bugs |
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On 08/07/2014 10:19 AM, Joonsoo Kim wrote: >> Is it needed to disable the pcp list? Shouldn't drain be enough? >> After the drain you already are sure that future freeing will see >> MIGRATE_ISOLATE and skip pcp list anyway, so why disable it >> completely? > > Yes, it is needed. Until we move freepages from normal buddy list > to isolate buddy list, freepages could be allocated by others. In this > case, they could be moved to pcp list. When it is flushed from pcp list > to buddy list, we need to check whether it is on isolate migratetype > pageblock or not. But, we don't want that hook in free_pcppages_bulk() > because it is page allocator's normal freepath. To remove it, we shoule > disable the pcp list here.
Ah, right. I thought that everything going to pcp lists would be through freeing which would already observe the isolate migratetype and skip pcplist. I forgot about the direct filling of pcplists from buddy list. You're right that we don't want extra hooks there.
Still, couldn't this be solved in a simpler way via another pcplist drain after the pages are moved from normal to isolate buddy list? Should be even faster because instead of disable - drain - enable (5 all-cpu kicks, since each pageset_update does 2 kicks) you have drain - drain (2 kicks). While it's true that pageset_update is single-zone operation, I guess we would easily benefit from having a single-zone drain operation as well.
Vlastimil
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