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Date: Thu, 28 Mar 2024 15:09:00 -0400
From: Johannes Weiner <hannes@cmpxchg.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Nhat Pham <nphamcs@gmail.com>,
	Chengming Zhou <chengming.zhou@linux.dev>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/9] mm: zswap: always shrink in zswap_store() if
 zswap_pool_reached_full
Message-ID: <20240328190900.GD7597@cmpxchg.org>
References: <20240325235018.2028408-1-yosryahmed@google.com>
 <20240325235018.2028408-2-yosryahmed@google.com>
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In-Reply-To: <20240325235018.2028408-2-yosryahmed@google.com>

On Mon, Mar 25, 2024 at 11:50:09PM +0000, Yosry Ahmed 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.
> - 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.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>