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

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Date: Fri, 9 Feb 2024 12:50:41 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
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 2024/2/9 05:09, Andrew Morton wrote:
> 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

It's correct. Thanks!

The other patch that includes optimization and cleanup is updated based on
mm-unstable and just resend:

https://lore.kernel.org/all/20240209044112.3883835-1-chengming.zhou@linux.dev/

> 
> --- 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
> 
>