linux-kernel - Re: [PATCH] zswap: do not allocate from atomic pool

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Date:   Mon, 21 Nov 2022 22:16:28 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Nhat Pham <nphamcs@...il.com>,
        Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zswap: do not allocate from atomic pool

On Tue, Nov 22, 2022 at 10:33:38AM +0900, Sergey Senozhatsky wrote:
> zswap_frontswap_load() should be called from preemptible
> context (we even call mutex_lock() there) and it does not
> look like we need to do GFP_ATOMIC allocaion for temp
> buffer there. Use GFP_KERNEL instead.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  mm/zswap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 2d69c1d678fe..f6c89049cf70 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1314,7 +1314,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>  	}
>  
>  	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> -		tmp = kmalloc(entry->length, GFP_ATOMIC);
> +		tmp = kmalloc(entry->length, GFP_KERNEL);

There is another one in zswap_writeback_entry() that seems equally
arbitrary. They came in through the same commit, with no further
explanation as to this choice. Do you want to pick that up too?