linux-kernel - Re: [PATCH mm-hotfixes-unstable] mm/zswap: invalidate duplicate entry when !zswap

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Date: Thu, 8 Feb 2024 13:09:52 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: chengming.zhou@...ux.dev
Cc: hannes@...xchg.org, yosryahmed@...gle.com, nphamcs@...il.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, Chengming Zhou
 <zhouchengming@...edance.com>, stable@...r.kernel.org
Subject: Re: [PATCH mm-hotfixes-unstable] mm/zswap: invalidate duplicate
 entry when !zswap_enabled

On Thu,  8 Feb 2024 02:32:54 +0000 chengming.zhou@...ux.dev wrote:

> From: Chengming Zhou <zhouchengming@...edance.com>
> 
> We have to invalidate any duplicate entry even when !zswap_enabled
> since zswap can be disabled anytime. If the folio store success before,
> then got dirtied again but zswap disabled, we won't invalidate the old
> duplicate entry in the zswap_store(). So later lru writeback may
> overwrite the new data in swapfile.
> 
> ...
>
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1516,7 +1516,7 @@ bool zswap_store(struct folio *folio)
>  	if (folio_test_large(folio))
>  		return false;
>  
> -	if (!zswap_enabled || !tree)
> +	if (!tree)
>  		return false;
>  
>  	/*
> @@ -1531,6 +1531,10 @@ bool zswap_store(struct folio *folio)
>  		zswap_invalidate_entry(tree, dupentry);
>  	}
>  	spin_unlock(&tree->lock);
> +
> +	if (!zswap_enabled)
> +		return false;
> +
>  	objcg = get_obj_cgroup_from_folio(folio);
>  	if (objcg && !obj_cgroup_may_zswap(objcg)) {
>  		memcg = get_mem_cgroup_from_objcg(objcg);

OK, thanks.

I saw only one reject from mm-unstable patches.  Your patch "mm/zswap:
make sure each swapfile always have zswap rb-tree" now does

--- a/mm/zswap.c~mm-zswap-make-sure-each-swapfile-always-have-zswap-rb-tree
+++ a/mm/zswap.c
@@ -1518,9 +1518,6 @@ bool zswap_store(struct folio *folio)
 	if (folio_test_large(folio))
 		return false;
 
-	if (!tree)
-		return false;
-
 	/*
 	 * If this is a duplicate, it must be removed before attempting to store
 	 * it, otherwise, if the store fails the old page won't be removed from