linux-kernel - Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams

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Message-ID: <ramywnizfouh7iimkcbvpzeevzdveljwcplyptvica4vsd6b4c@lfjfezhq6hwq>
Date: Thu, 6 Feb 2025 21:26:54 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Kairui Song <ryncsn@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams

On (25/02/03 21:00), Yosry Ahmed wrote:
> On Mon, Feb 03, 2025 at 12:49:42PM +0900, Sergey Senozhatsky wrote:
> > On (25/02/01 17:21), Kairui Song wrote:
> FWIW, I am not familiar at all with the zram code but zswap uses per-CPU
> acomp contexts with a mutex instead of a spinlock. So the task uses the
> context of the CPU that it started on, but it can be preempted or
> migrated and end up running on a different CPU.

Thank you for the idea.  We couldn't do that before (in zram), in a
number of cases per-CPU stream was taken from atomic context (under
zram table entry spinlock/bit-spinlock), but it's possible now
because entry lock is preemptible.