Received-SPF: pass (google.com: domain of linux-kernel+bounces-48834-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240201-b4-zswap-invalidate-entry-v1-0-56ed496b6e55@bytedance.com>
 <20240201-b4-zswap-invalidate-entry-v1-2-56ed496b6e55@bytedance.com>
In-Reply-To: <20240201-b4-zswap-invalidate-entry-v1-2-56ed496b6e55@bytedance.com>
From: Nhat Pham <nphamcs@gmail.com>
Date: Thu, 1 Feb 2024 12:56:20 -0800
Message-ID: <CAKEwX=MCr8qAbDhREWdVdLMujso7+JNoBozfDWLx5cqoMWhNiA@mail.gmail.com>
Subject: Re: [PATCH 2/6] mm/zswap: invalidate zswap entry when swap entry free
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, 
	Yosry Ahmed <yosryahmed@google.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Feb 1, 2024 at 7:50=E2=80=AFAM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> During testing I found there are some times the zswap_writeback_entry()
> return -ENOMEM, which is not we expected:
>
> bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=3Dcount()}'
> @[-12]: 1563
> @[0]: 277221
>
> The reason is that __read_swap_cache_async() return NULL because
> swapcache_prepare() failed. The reason is that we won't invalidate
> zswap entry when swap entry freed to the per-cpu pool, these zswap
> entries are still on the zswap tree and lru list.
>
> This patch moves the invalidation ahead to when swap entry freed
> to the per-cpu pool, since there is no any benefit to leave trashy
> zswap entry on the tree and lru list.
>
> With this patch:
> bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=3Dcount()}'
> @[0]: 259744

Nice!
Reviewed-by: Nhat Pham <nphamcs@gmail.com>