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

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Message-Id: <20241209181341.fb579d7c0f9d76ae7854c4fa@linux-foundation.org>
Date: Mon, 9 Dec 2024 18:13:41 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: 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, chenridong@...wei.com,
 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 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.