Re: [RFC PATCH 1/9] mm: zswap: always shrink in zswap_store() if zswap_pool_reached_full

Johannes Weiner
2024-03-28T19:09:02Z

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>