linux-kernel - Re: [PATCH v2] zram: easy the allocation of zcomp

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Message-ID: <20240207014442.GI69174@google.com>
Date: Wed, 7 Feb 2024 10:44:42 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Barry Song <21cnbao@...il.com>, Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: axboe@...nel.dk, linux-block@...r.kernel.org, senozhatsky@...omium.org,
	linux-kernel@...r.kernel.org, zhengtangquan@...o.com,
	Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v2] zram: easy the allocation of zcomp_strm's buffers
 through vmalloc

On (24/02/07 09:25), Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> Firstly, there is no need to keep zcomp_strm's buffers contiguous
> physically.
> 
> Secondly, The recent mTHP project has provided the possibility to
> swapout and swapin large folios. Compressing/decompressing large
> blocks can hugely decrease CPU consumption and improve compression
> ratio. This requires us to make zRAM support the compression and
> decompression for large objects.
> With the support of large objects in zRAM of our out-of-tree code,
> we have observed many allocation failures during CPU hotplug as
> large objects need larger buffers. So this change is also more
> future-proof once we begin to bring up multiple sizes in zRAM.
> 
> Signed-off-by: Barry Song <v-songbaohua@...o.com>

Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>

Note:
Taking it in NOT because of the out-of-tree code (we don't really
do that), but because this is executed from CPU offline/online
paths, which can happen on devices with fragmented memory (a valid
concern IMHO).

Minchan, if you have any objections, please chime in.

> @@ -37,7 +38,7 @@ static void zcomp_strm_free(struct zcomp_strm *zstrm)
>  {
>  	if (!IS_ERR_OR_NULL(zstrm->tfm))
>  		crypto_free_comp(zstrm->tfm);
> -	free_pages((unsigned long)zstrm->buffer, 1);
> +	vfree(zstrm->buffer);
>  	zstrm->tfm = NULL;
>  	zstrm->buffer = NULL;
>  }
> @@ -53,7 +54,7 @@ static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
>  	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
>  	 * case when compressed size is larger than the original one
>  	 */
> -	zstrm->buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
> +	zstrm->buffer = vzalloc(2 * PAGE_SIZE);
>  	if (IS_ERR_OR_NULL(zstrm->tfm) || !zstrm->buffer) {
>  		zcomp_strm_free(zstrm);
>  		return -ENOMEM;
> -- 
> 2.34.1
>