Re: [patch] mm, thp: do not perform sync compaction on pagefault

[Joonsoo Kim]

2014-05-01 9:45 GMT+09:00 David Rientjes <rientjes@xxxxxxxxxx>:
> Synchronous memory compaction can be very expensive: it can iterate an enormous
> amount of memory without aborting and it can wait on page locks and writeback to
> complete if a pageblock cannot be defragmented.
> Unfortunately, it's too expensive for pagefault for transparent hugepages and
> it's much better to simply fallback to pages.  On 128GB machines, we find that
> synchronous memory compaction can take O(seconds) for a single thp fault.

Hello,

AFAIK, synchronous compaction doesn't wait the page on writeback.
sync compaction pass MIGRATE_SYNC_LIGHT for migrate_mode,
instead of MIGRATE_SYNC. It results in skipping the page on writeback.

Thanks.
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