From: Alistair Popple <apopple@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, jgg@nvidia.com, minchan@kernel.org,
linux-kernel@vger.kernel.org, jhubbard@nvidia.com,
pasha.tatashin@soleen.com, david@redhat.com
Subject: Re: [PATCH v2] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes
Date: Thu, 04 Aug 2022 10:12:59 +1000 [thread overview]
Message-ID: <87czdg7tlt.fsf@nvdebian.thelocal> (raw)
In-Reply-To: <20220802171215.3c909e1984ec345ff94af155@linux-foundation.org>
Andrew Morton <akpm@linux-foundation.org> writes:
> On Tue, 2 Aug 2022 10:30:12 +1000 Alistair Popple <apopple@nvidia.com> wrote:
>
>> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages()
>> is called to migrate pages out of zones which should not contain any
>> longterm pinned pages.
>>
>> When migration succeeds all pages will have been unpinned so pinning
>> needs to be retried. This is indicated by returning zero. When all pages
>> are in the correct zone the number of pinned pages is returned.
>>
>> However migration can also fail, in which case pages are unpinned and
>> -ENOMEM is returned. However if the failure was due to not being unable
>> to isolate a page zero is returned. This leads to indefinite looping in
>> __gup_longterm_locked().
>>
>> Fix this by simplifying the return codes such that zero indicates all
>> pages were successfully pinned in the correct zone while errors indicate
>> either pages were migrated and pinning should be retried or that
>> migration has failed and therefore the pinning operation should fail.
>>
>> This fixes the indefinite looping on page isolation failure by failing
>> the pin operation instead of retrying indefinitely.
>>
>
> Are we able to identify a Fixes: for this? Presumably something in the
> series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"?
It seems the infinite loop was desired behaviour so I will re-spin this
as a pure clean-up.
next prev parent reply other threads:[~2022-08-04 0:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-02 0:30 [PATCH v2] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes Alistair Popple
2022-08-02 13:50 ` Jason Gunthorpe
2022-08-02 21:36 ` Pasha Tatashin
2022-08-04 0:01 ` Alistair Popple
2022-08-03 0:12 ` Andrew Morton
2022-08-04 0:12 ` Alistair Popple [this message]
2022-08-04 7:40 ` David Hildenbrand
2022-08-04 9:57 ` Alistair Popple
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