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Date: Wed, 21 Feb 2024 23:22:43 +0100
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Subject: Re: [PATCH 1/2] mm: compaction: limit the suitable target page order
 to be less than cc->order
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To: Andrew Morton <akpm@linux-foundation.org>,
 Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>, mgorman@techsingularity.net, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
References: <afcd9377351c259df7a25a388a4a0d5862b986f4.1705928395.git.baolin.wang@linux.alibaba.com>
 <20c8fa7c-62ae-4e48-aaec-8b512519cee9@suse.cz>
 <5277627F-6791-46A1-AFC2-54FBF0DABF1A@nvidia.com>
 <83bc1070-2eb4-4fac-aecf-9cc407003ca2@linux.alibaba.com>
 <20240221141504.3c3cec674553b4df4bd72ec1@linux-foundation.org>
From: Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20240221141504.3c3cec674553b4df4bd72ec1@linux-foundation.org>
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On 2/21/24 23:15, Andrew Morton wrote:
> On Mon, 19 Feb 2024 10:55:59 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
>> 
>> >>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> >>
>> >> I doubt this will make much difference, because if such a larger order free
>> >> page exists, we shouldn't have a reason to be compacting for a lower order
>> >> in the first place?
>> > 
>> > Unless kswapd gets us such a free block in the background right after
>> > get_page_from_freelist() and before compaction finishes in the allocation
>> > slow path.
>> > 
>> > If this happens often and cc->order is not -1, it might be better to stop
>> > compaction and get_page_from_freelist() to save cycles on unnecessary pfn
>> > scanning. For completeness, when cc->order == -1, the logic does not change.
>> 
>> Yes, this is one possible case. There are also some other concurrent 
>> scenarios, such as when compaction is running (after 
>> compaction_suitable()), at the same time, other applications release a 
>> large folio to the free list. In this case, the free large folio 
>> scanning should also be avoided.
> 
> This went quiet.
> 
> We have an ack from Mel.  Are people OK with sending this change
> upstream?

It's not wrong, so I'm OK.