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Date: Thu, 2 Nov 2017 13:04:33 +0000 From: Mel Gorman <mgorman@...hsingularity.net> To: Vlastimil Babka <vbabka@...e.cz> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com> Subject: Re: [PATCH 1/3] mm, compaction: extend pageblock_skip_persistent() to all compound pages On Thu, Nov 02, 2017 at 01:17:04PM +0100, Vlastimil Babka wrote: > The pageblock_skip_persistent() function checks for HugeTLB pages of pageblock > order. When clearing pageblock skip bits for compaction, the bits are not > cleared for such pageblocks, because they cannot contain base pages suitable > for migration, nor free pages to use as migration targets. > > This optimization can be simply extended to all compound pages of order equal > or larger than pageblock order, because migrating such pages (if they support > it) cannot help sub-pageblock fragmentation. This includes THP's and also > gigantic HugeTLB pages, which the current implementation doesn't persistently > skip due to a strict pageblock_order equality check and not recognizing tail > pages. > > While THP pages are generally less "persistent" than HugeTLB, we can still > expect that if a THP exists at the point of __reset_isolation_suitable(), it > will exist also during the subsequent compaction run. The time difference here > could be actually smaller than between a compaction run that sets a > (non-persistent) skip bit on a THP, and the next compaction run that observes > it. > > Signed-off-by: Vlastimil Babka <vbabka@...e.cz> Acked-by: Mel Gorman <mgorman@...hsingularity.net> -- Mel Gorman SUSE Labs
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