linux-kernel - Re: [RFC PATCH 1/6] mm/mmu_notifier: Allow multiple struct mmu_interval

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Message-ID: <aKNYUaPS0PiRk/yj@lstrano-desk.jf.intel.com>
Date: Mon, 18 Aug 2025 09:44:01 -0700
From: Matthew Brost <matthew.brost@...el.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
	<intel-xe@...ts.freedesktop.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Simona Vetter <simona.vetter@...ll.ch>, Dave Airlie <airlied@...il.com>,
	<dri-devel@...ts.freedesktop.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, Christian König
	<christian.koenig@....com>
Subject: Re: [RFC PATCH 1/6] mm/mmu_notifier: Allow multiple struct
 mmu_interval_notifier passes

On Mon, Aug 18, 2025 at 01:36:17PM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 18, 2025 at 09:25:20AM -0700, Matthew Brost wrote:
> > I think this choice makes sense: it allows embedding the wait state from
> > the initial notifier call into the pass structure. Patch [6] shows this
> > by attaching the issued TLB invalidation fences to the pass. Since a
> > single notifier may be invoked multiple times with different ranges but
> > the same seqno,
> 
> That should be explained, but also seems to be a bit of a different
> issue..
> 
> If the design is really to only have two passes and this linked list
> is about retaining state then there should not be so much freedom to
> have more passes.

I’ll let Thomas weigh in on whether we really need more than two passes;
my feeling is that two passes are likely sufficient. It’s also worth
noting that the linked list has an added benefit: the notifier tree only
needs to be walked once (a small time-complexity win).

Matt

> 
> Jason