linux-kernel - Re: [PATCH 1/2] mm/zswap: don't return LRU

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Message-ID: <20240126142800.GF1567330@cmpxchg.org>
Date: Fri, 26 Jan 2024 09:28:00 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: chengming.zhou@...ux.dev
Cc: yosryahmed@...gle.com, nphamcs@...il.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH 1/2] mm/zswap: don't return LRU_SKIP if we have dropped
 lru lock

On Fri, Jan 26, 2024 at 08:30:14AM +0000, chengming.zhou@...ux.dev wrote:
> From: Chengming Zhou <zhouchengming@...edance.com>
> 
> 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.

Good catch. Can you mention the possible consequences in the log?

"Otherwise, the iteration might continue from a cursor position that
was freed while the locks were dropped."?

> 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")
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

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