Received-SPF: pass (google.com: domain of linux-kernel+bounces-43659-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Tue, 30 Jan 2024 00:09:04 +0000
In-Reply-To: <20240126-zswap-writeback-race-v2-1-b10479847099@bytedance.com>
Precedence: bulk
Mime-Version: 1.0
References: <20240126-zswap-writeback-race-v2-0-b10479847099@bytedance.com> <20240126-zswap-writeback-race-v2-1-b10479847099@bytedance.com>
Message-ID: <Zbg-INqi9oMUqJaW@google.com>
Subject: Re: [PATCH v2 1/3] mm/zswap: don't return LRU_SKIP if we have dropped
 lru lock
From: Yosry Ahmed <yosryahmed@google.com>
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Nhat Pham <nphamcs@gmail.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Chris Li <chriscli@google.com>, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Content-Type: text/plain; charset="us-ascii"

On Sun, Jan 28, 2024 at 01:28:49PM +0000, Chengming Zhou wrote:
> LRU_SKIP can only be returned if we don't ever dropped lru lock, or
> we need to return LRU_RETRY to restart from the head of lru list.
> 
> Otherwise, the iteration might continue from a cursor position that
> was freed while the locks were dropped.

Does this warrant a stable backport?

> 
> Actually we may need to introduce another LRU_STOP to really terminate
> the ongoing shrinking scan process, when we encounter a warm page
> already in the swap cache. The current list_lru implementation
> doesn't have this function to early break from __list_lru_walk_one.
> 
> Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Nhat Pham <nphamcs@gmail.com>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>

Acked-by: Yosry Ahmed <yosryahmed@google.com>