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Date: Mon, 20 Apr 2020 20:26:15 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Nitin Gupta <nigupta@...dia.com> Cc: Mel Gorman <mgorman@...hsingularity.net>, Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>, Matthew Wilcox <willy@...radead.org>, Mike Kravetz <mike.kravetz@...cle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, David Rientjes <rientjes@...gle.com>, Nitin Gupta <nitin@...ingupta.dev>, linux-kernel <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Linux API <linux-api@...r.kernel.org> Subject: Re: [PATCH v3] mm: Proactive compaction On Tue, 10 Mar 2020 15:25:39 -0700 Nitin Gupta <nigupta@...dia.com> wrote: > For some applications we need to allocate almost all memory as > hugepages. However, on a running system, higher order allocations can > fail if the memory is fragmented. Linux kernel currently does on-demand > compaction as we request more hugepages but this style of compaction > incurs very high latency. Experiments with one-time full memory > compaction (followed by hugepage allocations) shows that kernel is able > to restore a highly fragmented memory state to a fairly compacted memory > state within <1 sec for a 32G system. Such data suggests that a more > proactive compaction can help us allocate a large fraction of memory as > hugepages keeping allocation latencies low. hn, there was plenty of feedback for earlier versions, but then everyone went quiet. I guess it's time for a refresh and resend, please. With some code comments, please! Is the code really so self-evident that this: +/* Compact all zones within a node according to proactiveness */ is the only thing which needs to be said about it? How is the reader to know what proactive compaction actually *is*? What does extfrag_for_order() do and what does its return value mean? Please document /sys/kernel/mm/compaction/proactiveness in the appropriate place under Documentation/
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