linux-kernel - Re: [RFC PATCH 1/9] mm: zswap: always shrink in zswap_store() if zswap_pool_reached

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Message-ID: <CAKEwX=PXUCnubYJEzF0wKU3B1aVGm3oS4EFmtMXUj4LsPyLK8A@mail.gmail.com>
Date: Tue, 26 Mar 2024 14:49:30 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/9] mm: zswap: always shrink in zswap_store() if zswap_pool_reached_full

On Mon, Mar 25, 2024 at 4:50 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> The cleanup code in zswap_store() is not pretty, particularly the
> 'shrink' label at the bottom that ends up jumping between cleanup
> labels.
>
> Instead of having a dedicated label to shrink the pool, just use
> zswap_pool_reached_full directly to figure out if the pool needs
> shrinking. zswap_pool_reached_full should be true if and only if the
> pool needs shrinking.
>
> The only caveat is that the value of zswap_pool_reached_full may be
> changed by concurrent zswap_store() calls between checking the limit and
> testing zswap_pool_reached_full in the cleanup code. This is fine
> because:
> - If zswap_pool_reached_full was true during limit checking then became
>   false during the cleanup code, then someone else already took care of
>   shrinking the pool and there is no need to queue the worker. That
>   would be a good change.

Yup.

> - If zswap_pool_reached_full was false during limit checking then became
>   true during the cleanup code, then someone else hit the limit
>   meanwhile. In this case, both threads will try to queue the worker,
>   but it never gets queued more than once anyway. Also, calling
>   queue_work() multiple times when the limit is hit could already happen
>   today, so this isn't a significant change in any way.

Agree.

>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

This change by itself seems fine to me.
Reviewed-by: Nhat Pham <nphamcs@...il.com>