From: Christoph Hellwig <hch@infradead.org>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jason Gunthorpe <jgg@nvidia.com>,
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>,
Alistair Popple <apopple@nvidia.com>,
Pak Markthub <pmarkthub@nvidia.com>
Subject: Re: [RFC] RDMA/umem: pin_user_pages*() can temporarily fail due to migration glitches
Date: Tue, 30 Apr 2024 22:10:43 -0700 [thread overview]
Message-ID: <ZjHO04Rb75TIlmkA@infradead.org> (raw)
In-Reply-To: <20240501003117.257735-1-jhubbard@nvidia.com>
> + pinned = -ENOMEM;
> + int attempts = 0;
> + /*
> + * pin_user_pages_fast() can return -EAGAIN, due to falling back
> + * to gup-slow and then failing to migrate pages out of
> + * ZONE_MOVABLE due to a transient elevated page refcount.
> + *
> + * One retry is enough to avoid this problem, so far, but let's
> + * use a slightly higher retry count just in case even larger
> + * systems have a longer-lasting transient refcount problem.
> + *
> + */
> + static const int MAX_ATTEMPTS = 3;
> +
> + while (pinned == -EAGAIN && attempts < MAX_ATTEMPTS) {
> + pinned = pin_user_pages_fast(cur_base,
> + min_t(unsigned long,
> + npages, PAGE_SIZE /
> + sizeof(struct page *)),
> + gup_flags, page_list);
> ret = pinned;
> - goto umem_release;
> + attempts++;
> +
> + if (pinned == -EAGAIN)
> + continue;
> }
> + if (pinned < 0)
> + goto umem_release;
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.
next prev parent reply other threads:[~2024-05-01 5:10 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 [this message]
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
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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