linux-kernel - Re: [PATCH v6 02/17] zram: permit preemption with active compression stream

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Message-ID: <Z7d-FawfAYRQJUgn@google.com>
Date: Thu, 20 Feb 2025 19:10:13 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Hillf Danton <hdanton@...a.com>, Kairui Song <ryncsn@...il.com>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 02/17] zram: permit preemption with active compression
 stream

On Fri, Feb 14, 2025 at 01:50:14PM +0900, Sergey Senozhatsky wrote:
> Currently, per-CPU stream access is done from a non-preemptible
> (atomic) section, which imposes the same atomicity requirements on
> compression backends as entry spin-lock, and makes it impossible
> to use algorithms that can schedule/wait/sleep during compression
> and decompression.
> 
> Switch to preemptible per-CPU model, similar to the one used
> in zswap.  Instead of a per-CPU local lock, each stream carries
> a mutex which is locked throughout entire time zram uses it
> for compression or decompression, so that cpu-dead event waits
> for zram to stop using a particular per-CPU stream and release
> it.
> 
> Suggested-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>

Reviewed-by: Yosry Ahmed <yosry.ahmed@...ux.dev>