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

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Message-ID: <20240106013021.GA123449@google.com>
Date: Sat, 6 Jan 2024 10:30:21 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Barry Song <21cnbao@...il.com>
Cc: minchan@...nel.org, senozhatsky@...omium.org, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	Barry Song <v-songbaohua@...o.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] zram: easy the allocation of zcomp_strm's buffers with 2
 pages

On (24/01/03 13:30), Barry Song wrote:
> There is no need to keep zcomp_strm's buffers contiguous physically.
> And rarely, 1-order allocation can fail while buddy is seriously
> fragmented.

Dunno. Some of these don't sound like convincing reasons, I'm afraid.
We don't allocate compression streams all the time, we do it once
per-CPU. And if the system is under such a terrible memory pressure
then one probably should not use zram at all, because zsmalloc needs
pages for its pool.

I also wonder whether Android uses HW compression, in which case we
may need to have physically contig pages. Not to mention TLB shootdowns
that virt contig pages add to the picture.

[..]
> @@ -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;