From: John Hubbard <jhubbard@nvidia.com>
To: Alistair Popple <apopple@nvidia.com>, Jason Gunthorpe <jgg@nvidia.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-rdma@vger.kernel.org, linux-mm@kvack.org,
Mike Marciniszyn <mike.marciniszyn@intel.com>,
Leon Romanovsky <leon@kernel.org>,
Artemy Kovalyov <artemyko@nvidia.com>,
Michael Guralnik <michaelgur@nvidia.com>,
Pak Markthub <pmarkthub@nvidia.com>
Subject: Re: [RFC] RDMA/umem: pin_user_pages*() can temporarily fail due to migration glitches
Date: Wed, 1 May 2024 23:49:48 -0700 [thread overview]
Message-ID: <79a63282-867f-41d9-988e-ff6ae70d3d9b@nvidia.com> (raw)
In-Reply-To: <87r0el3tfi.fsf@nvdebian.thelocal>
On 5/1/24 6:05 PM, Alistair Popple wrote:
> Jason Gunthorpe <jgg@nvidia.com> writes:
>> On Tue, Apr 30, 2024 at 10:10:43PM -0700, Christoph Hellwig wrote:
...
>>> This doesn't make sense. IFF a blind retry is all that is needed it
>>> should be done in the core functionality. I fear it's not that easy,
>>> though.
>>
>> +1
>>
>> This migration retry weirdness is a GUP issue, it needs to be solved
>> in the mm not exposed to every pin_user_pages caller.
>>
>> If it turns out ZONE_MOVEABLE pages can't actually be reliably moved
>> then it is pretty broken..
>
> I wonder if we should remove the arbitrary retry limit in
> migrate_pages() entirely for ZONE_MOVEABLE pages and just loop until
> they migrate? By definition there should only be transient references on
> these pages so why do we need to limit the number of retries in the
> first place?
>
Well, along those lines, I can confirm that this patch also fixes the
symptoms:
diff --git a/mm/migrate.c b/mm/migrate.c
index 73a052a382f1..faa67cc441e2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1728,7 +1728,9 @@ static int migrate_pages_batch(struct list_head *from,
else
goto move;
case -EAGAIN:
- retry++;
+ /* For ZONE_MOVABLE folios, retry forever */
+ if (!folio_is_zone_movable(folio))
+ retry++;
thp_retry += is_thp;
nr_retry_pages += nr_pages;
break;
@@ -1786,7 +1788,9 @@ static int migrate_pages_batch(struct list_head *from,
*/
switch(rc) {
case -EAGAIN:
- retry++;
+ /* For ZONE_MOVABLE folios, retry forever */
+ if (!folio_is_zone_movable(folio))
+ retry++;
thp_retry += is_thp;
nr_retry_pages += nr_pages;
break;
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2024-05-02 6:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-01 0:31 [RFC] RDMA/umem: pin_user_pages*() can temporarily fail due to migration glitches John Hubbard
2024-05-01 5:10 ` Christoph Hellwig
2024-05-01 12:10 ` Jason Gunthorpe
2024-05-01 17:32 ` John Hubbard
2024-05-02 1:05 ` Alistair Popple
2024-05-02 6:49 ` John Hubbard [this message]
2024-05-02 6:56 ` David Hildenbrand
2024-05-02 18:10 ` John Hubbard
2024-05-02 18:34 ` Jason Gunthorpe
2024-05-02 18:44 ` Matthew Wilcox
2024-05-10 7:54 ` David Hildenbrand
2024-05-11 0:32 ` Kasireddy, Vivek
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