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

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Message-ID: <d34ba6c8c68a2fa85f052bdb4d27be15561f4861.camel@linux.intel.com>
Date: Mon, 18 Aug 2025 18:42:36 +0200
From: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Matthew Brost <matthew.brost@...el.com>
Cc: 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, 2025-08-18 at 13:36 -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.

Actually the initial suggestion was two passes only. Then I thought I
saw a use-case for even three passes and added the multi-pass thing,
but I think it turned out we didn't have such a use-case. IMO we could
restrict it to two-pass. Matthew, that should be completely OK for the
SVM use-case, right?

/Thomas


> 
> Jason