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Message-ID: <4b2f9a61-ca67-6a34-41c9-c191cac756b3@redhat.com>
Date:   Mon, 11 Jul 2022 16:00:54 +0200
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Subject: Re: [PATCH v8 07/15] mm/gup: migrate device coherent pages when
 pinning instead of failing
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To:     Matthew Wilcox <willy@infradead.org>
Cc:     Alex Sierra <alex.sierra@amd.com>, jgg@nvidia.com,
        Felix.Kuehling@amd.com, linux-mm@kvack.org, rcampbell@nvidia.com,
        linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        hch@lst.de, jglisse@redhat.com, apopple@nvidia.com,
        akpm@linux-foundation.org
References: <20220707190349.9778-1-alex.sierra@amd.com>
 <20220707190349.9778-8-alex.sierra@amd.com>
 <2c4dd559-4fa9-f874-934f-d6b674543d0f@redhat.com>
 <Ysws7LOirtQ07JG/@casper.infradead.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <Ysws7LOirtQ07JG/@casper.infradead.org>
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On 11.07.22 16:00, Matthew Wilcox wrote:
> On Mon, Jul 11, 2022 at 03:35:42PM +0200, David Hildenbrand wrote:
>>> +		/*
>>> +		 * Device coherent pages are managed by a driver and should not
>>> +		 * be pinned indefinitely as it prevents the driver moving the
>>> +		 * page. So when trying to pin with FOLL_LONGTERM instead try
>>> +		 * to migrate the page out of device memory.
>>> +		 */
>>> +		if (folio_is_device_coherent(folio)) {
>>> +			WARN_ON_ONCE(PageCompound(&folio->page));
>>
>> Maybe that belongs into migrate_device_page()?
> 
> ... and should be simply WARN_ON_ONCE(folio_test_large(folio)).
> No need to go converting it back into a page in order to test things
> that can't possibly be true.
> 

Good point.

-- 
Thanks,

David / dhildenb