linux-kernel - Re: [External] Re: [PATCH] mm: zswap: fix the lack of page lru flag in zswap_writeback

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Message-ID: <CAKEwX=NuXR9Ot1eRFsp9n-3Tq9yhjD9up+jyvXeOzQ4xK9kEPA@mail.gmail.com>
Date: Sun, 7 Jan 2024 13:29:11 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Zhongkun He <hezhongkun.hzk@...edance.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosryahmed@...gle.com, 
	sjenning@...hat.com, ddstreet@...e.org, vitaly.wool@...sulko.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Chris Li <chrisl@...nel.org>, weijie.yang@...sung.com
Subject: Re: [External] Re: [PATCH] mm: zswap: fix the lack of page lru flag
 in zswap_writeback_entry

On Fri, Jan 5, 2024 at 6:10 AM Zhongkun He <hezhongkun.hzk@...edance.com> wrote:
>
> > > There is another option here, which is not to move the page to the
> > > tail of the inactive
> > > list after end_writeback and delete the following code in
> > > zswap_writeback_entry(),
> > > which did not work properly. But the pages will not be released first.
> > >
> > > /* move it to the tail of the inactive list after end_writeback */
> > > SetPageReclaim(page);

Ok, so I took a look at the patch that originally introduced this
piece of logic:

https://github.com/torvalds/linux/commit/b349acc76b7f65400b85abd09a5379ddd6fa5a97

Looks like it's not for the sake of correctness, but only as a
best-effort optimization (reducing page scanning). If it doesn't bring
any benefit (i.e due to the newly allocated page still on the cpu
batch), then we can consider removing it. After all, if you're right
and it's not really doing anything here - why bother. Perhaps we can
replace this with some other mechanism to avoid it being scanned for
reclaim.

I would cc Weijie as well, as he is the original author of this.