linux-kernel - Re: [RFC PATCH 1/4] mm: use current as mmu notifier's owner

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Message-ID: <20250814172018.GJ802098@nvidia.com>
Date: Thu, 14 Aug 2025 14:20:18 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Mika Penttilä <mpenttil@...hat.com>,
	Alistair Popple <apopple@...dia.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Balbir Singh <balbirs@...dia.com>
Subject: Re: [RFC PATCH 1/4] mm: use current as mmu notifier's owner

On Thu, Aug 14, 2025 at 08:00:01PM +0300, Mika Penttilä wrote:
> as well as hmm test module with :
> 
>          * Ignore invalidation callbacks for device private pages since
>          * the invalidation is handled as part of the migration process.
>          */
>         if (range->event == MMU_NOTIFY_MIGRATE &&
>             range->owner == dmirror->mdevice)
>                 return true;

If I recall this was about a very specific case where migration does a
number of invalidations and some of the earlier ones are known to be
redundant in this specific case. Redundant means it can be ignored
without causing an inconsistency.

Alistair would know, but I assumed this works OK because the above
invalidation doesn't actually go on to free any pages but keeps them
around until a later invalidation?

This is nothing like what your case is talking about.

Jason