linux-kernel - Re: [PATCH RFC 04/29] fsverity: add per-sb workqueue for post read processing

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Message-ID: <aJotnxPj_OXkrc42@slm.duckdns.org>
Date: Mon, 11 Aug 2025 07:51:27 -1000
From: Tejun Heo <tj@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Andrey Albershteyn <aalbersh@...hat.com>, fsverity@...ts.linux.dev,
	linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
	david@...morbit.com, djwong@...nel.org, ebiggers@...nel.org,
	Lai Jiangshan <jiangshanlai@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 04/29] fsverity: add per-sb workqueue for post read
 processing

Hello,

On Mon, Aug 11, 2025 at 01:45:19PM +0200, Christoph Hellwig wrote:
> On Mon, Jul 28, 2025 at 10:30:08PM +0200, Andrey Albershteyn wrote:
> > From: Andrey Albershteyn <aalbersh@...hat.com>
> > 
> > For XFS, fsverity's global workqueue is not really suitable due to:
> > 
> > 1. High priority workqueues are used within XFS to ensure that data
> >    IO completion cannot stall processing of journal IO completions.
> >    Hence using a WQ_HIGHPRI workqueue directly in the user data IO
> >    path is a potential filesystem livelock/deadlock vector.
> 
> Do they?  I though the whole point of WQ_HIGHPRI was that they'd
> have separate rescue workers to avoid any global pool effects.

HIGHPRI and MEM_RECLAIM are orthogonal. HIGHPRI makes the workqueue use
worker pools with high priority, so all work items would execute at MIN_NICE
(-20). Hmm... actually, rescuer doesn't set priority according to the
workqueue's, which seems buggy.

Thanks.

-- 
tejun