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Date: Thu, 15 Feb 2024 17:52:24 +0100
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Subject: Re: [PATCH v5 3/3] mm/compaction: optimize >0 order folio compaction
 with free page split.
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To: Zi Yan <ziy@nvidia.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: "Huang, Ying" <ying.huang@intel.com>, Ryan Roberts
 <ryan.roberts@arm.com>, Andrew Morton <akpm@linux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@infradead.org>,
 David Hildenbrand <david@redhat.com>, "Yin, Fengwei"
 <fengwei.yin@intel.com>, Yu Zhao <yuzhao@google.com>,
 "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
 Johannes Weiner <hannes@cmpxchg.org>,
 Baolin Wang <baolin.wang@linux.alibaba.com>,
 Kemeng Shi <shikemeng@huaweicloud.com>,
 Mel Gorman <mgorman@techsingularity.net>, Rohan Puri
 <rohan.puri15@gmail.com>, Mcgrof Chamberlain <mcgrof@kernel.org>,
 Adam Manzanares <a.manzanares@samsung.com>,
 "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
References: <20240214220420.1229173-1-zi.yan@sent.com>
 <20240214220420.1229173-4-zi.yan@sent.com>
From: Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20240214220420.1229173-4-zi.yan@sent.com>
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On 2/14/24 23:04, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> During migration in a memory compaction, free pages are placed in an array
> of page lists based on their order.  But the desired free page order
> (i.e., the order of a source page) might not be always present, thus
> leading to migration failures and premature compaction termination.  Split
> a high order free pages when source migration page has a lower order to
> increase migration successful rate.
> 
> Note: merging free pages when a migration fails and a lower order free
> page is returned via compaction_free() is possible, but there is too much
> work.  Since the free pages are not buddy pages, it is hard to identify
> these free pages using existing PFN-based page merging algorithm.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Tested-by: Yu Zhao <yuzhao@google.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Thanks!