Re: [PATCH 5/6] mm, compaction: skip compound pages by order in free scanner

From: Joonsoo Kim
Date: Tue Jun 16 2015 - 01:43:10 EST

On Wed, Jun 10, 2015 at 11:32:33AM +0200, Vlastimil Babka wrote:
> The compaction free scanner is looking for PageBuddy() pages and skipping all
> others. For large compound pages such as THP or hugetlbfs, we can save a lot
> of iterations if we skip them at once using their compound_order(). This is
> generally unsafe and we can read a bogus value of order due to a race, but if
> we are careful, the only danger is skipping too much.
> When tested with stress-highalloc from mmtests on 4GB system with 1GB hugetlbfs
> pages, the vmstat compact_free_scanned count decreased by at least 15%.
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Acked-by: Joonsoo Kim <>

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