linux-kernel - Re: [PATCH v4 0/1] mm: vmascan: retry folios written back while isolated for traditional LRU

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Message-ID: <f6872957-07ea-4d3a-b10c-a302cd291fda@huawei.com>
Date: Tue, 10 Dec 2024 14:42:07 +0800
From: chenridong <chenridong@...wei.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Chen Ridong
	<chenridong@...weicloud.com>
CC: <mhocko@...e.com>, <hannes@...xchg.org>, <yosryahmed@...gle.com>,
	<yuzhao@...gle.com>, <david@...hat.com>, <willy@...radead.org>,
	<ryan.roberts@....com>, <baohua@...nel.org>, <21cnbao@...il.com>,
	<wangkefeng.wang@...wei.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <wangweiyang2@...wei.com>,
	<xieym_ict@...mail.com>
Subject: Re: [PATCH v4 0/1] mm: vmascan: retry folios written back while
 isolated for traditional LRU



On 2024/12/10 10:13, Andrew Morton wrote:
> On Mon,  9 Dec 2024 08:36:17 +0000 Chen Ridong <chenridong@...weicloud.com> wrote:
> 
>> The commit 359a5e1416ca ("mm: multi-gen LRU: retry folios written back
>> while isolated") only fixed the issue for mglru. However, this issue
>> also exists in the traditional active/inactive LRU. Fix this issue
>> in the same way for active/inactive lru.
>>
>> What is fixed:
>> The page reclaim isolates a batch of folios from the tail of one of the
>> LRU lists and works on those folios one by one.  For a suitable
>> swap-backed folio, if the swap device is async, it queues that folio for
>> writeback.  After the page reclaim finishes an entire batch, it puts back
>> the folios it queued for writeback to the head of the original LRU list.
>>
>> In the meantime, the page writeback flushes the queued folios also by
>> batches.  Its batching logic is independent from that of the page reclaim.
>> For each of the folios it writes back, the page writeback calls
>> folio_rotate_reclaimable() which tries to rotate a folio to the tail.
>>
>> folio_rotate_reclaimable() only works for a folio after the page reclaim
>> has put it back.  If an async swap device is fast enough, the page
>> writeback can finish with that folio while the page reclaim is still
>> working on the rest of the batch containing it.  In this case, that folio
>> will remain at the head and the page reclaim will not retry it before
>> reaching there.
> 
> For a single patch series I think it's best to just make it a single
> patch!  No need for a [0/n]: just put all the info into the patch's
> changelog.
> 
> The patch doesn't apply to current development kernels.  Please check
> the mm-unstable branch of
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/, or
> linux-next.
> 
> Please replace vmascan with vmscan in the title.

Thanks, Will update.

Best regards,
Ridong