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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Alistair Popple <apopple@nvidia.com>
Cc: rcampbell@nvidia.com, linux-doc@vger.kernel.org,
	nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
	linux-mm@kvack.org, bskeggs@redhat.com,
	akpm@linux-foundation.org
Subject: Re: [Nouveau] [PATCH 1/9] mm/migrate.c: Always allow device private pages to migrate
Date: Tue, 9 Feb 2021 09:39:32 -0400
Message-ID: <20210209133932.GD4718@ziepe.ca> (raw)
In-Reply-To: <20210209010722.13839-2-apopple@nvidia.com>

On Tue, Feb 09, 2021 at 12:07:14PM +1100, Alistair Popple wrote:
> Device private pages are used to represent device memory that is not
> directly accessible from the CPU. Extra references to a device private
> page are only used to ensure the struct page itself remains valid whilst
> waiting for migration entries. Therefore extra references should not
> prevent device private page migration as this can lead to failures to
> migrate pages back to the CPU which are fatal to the user process.

This should identify the extra references in expected_count, just
disabling this protection seems unsafe, ZONE_DEVICE is not so special
that the refcount means nothing

Is this a side effect of the extra refcounts that Ralph was trying to
get rid of? I'd rather see that work finished :)

Jason
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Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  1:07 [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 1/9] mm/migrate.c: Always allow device private pages to migrate Alistair Popple
2021-02-09 13:39   ` Jason Gunthorpe [this message]
2021-02-10  3:40     ` Alistair Popple
2021-02-10 12:56       ` Jason Gunthorpe
2021-02-09  1:07 ` [Nouveau] [PATCH 2/9] mm/migrate.c: Allow pfn flags to be passed to migrate_vma_setup() Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 3/9] mm/migrate: Add a unmap and pin migration mode Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 4/9] Documentation: Add unmap and pin to HMM Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 5/9] hmm-tests: Add test for unmap and pin Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 6/9] nouveau/dmem: Only map migrating pages Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 7/9] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 8/9] nouveau/dmem: Add support for multiple page types Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 9/9] nouveau/svm: Implement atomic SVM access Alistair Popple
2021-02-09 10:27 ` [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau Daniel Vetter
2021-02-09 12:57   ` Alistair Popple
2021-02-09 13:35     ` Jason Gunthorpe
2021-02-09 13:39       ` Daniel Vetter
2021-02-09 13:44         ` Jason Gunthorpe
2021-02-09 21:17       ` Jerome Glisse
2021-02-10 17:56         ` Jason Gunthorpe
2021-02-09 13:37     ` Daniel Vetter
2021-02-09 20:53       ` John Hubbard
2021-02-10 12:59         ` Daniel Vetter
2021-02-11  2:26           ` John Hubbard
2021-02-10 17:59         ` Jason Gunthorpe
2021-02-11  7:55           ` Christoph Hellwig
2021-02-17 23:00             ` Alistair Popple

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