From: Jan Kara <jack@suse.cz>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Dave Chinner" <david@fromorbit.com>,
"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 1/3] mm/gup: track FOLL_PIN pages
Date: Mon, 27 Jan 2020 12:06:24 +0100 [thread overview]
Message-ID: <20200127110624.GD19414@quack2.suse.cz> (raw)
In-Reply-To: <20200125021115.731629-2-jhubbard@nvidia.com>
On Fri 24-01-20 18:11:13, John Hubbard wrote:
> +static __maybe_unused struct page *try_grab_compound_head(struct page *page,
> + int refs,
> + unsigned int flags)
> +{
> + if (flags & FOLL_GET)
> + return try_get_compound_head(page, refs);
> + else if (flags & FOLL_PIN) {
> + int orig_refs = refs;
> +
> + /*
> + * When pinning a compound page of order > 1 (which is what
> + * hpage_pincount_available() checks for), use an exact count to
> + * track it, via hpage_pincount_inc/_dec().
> + *
> + * However, be sure to *also* increment the normal page refcount
> + * field at least once, so that the page really is pinned.
> + */
> + if (!hpage_pincount_available(page))
> + refs *= GUP_PIN_COUNTING_BIAS;
> +
> + page = try_get_compound_head(page, refs);
> + if (!page)
> + return NULL;
> +
> + if (hpage_pincount_available(page))
> + hpage_pincount_inc(page);
Umm, adding just 1 to pincount looks dangerous to me as
try_grab_compound_head() would not compose - you could not release
references acquired by try_grab_compound_head() with refs==2 by two calls
to put_compound_head() with refs==1. So I'd rather have here:
hpage_pincount_add(page, refs) and similarly in put_compound_head().
Otherwise the patch looks good to me from a quick look.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-01-27 11:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-25 2:11 [PATCH 0/3] mm/gup: track FOLL_PIN pages (follow on from v12) John Hubbard
2020-01-25 2:11 ` [PATCH 1/3] mm/gup: track FOLL_PIN pages John Hubbard
2020-01-27 11:06 ` Jan Kara [this message]
2020-01-27 18:17 ` John Hubbard
2020-01-27 13:00 ` Kirill A. Shutemov
2020-01-27 18:18 ` John Hubbard
2020-01-25 2:11 ` [PATCH 2/3] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-01-27 20:52 ` Nathan Chancellor
2020-01-27 21:32 ` John Hubbard
2020-01-25 2:11 ` [PATCH 3/3] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2020-01-25 16:23 ` [PATCH 0/3] mm/gup: track FOLL_PIN pages (follow on from v12) Leon Romanovsky
2020-01-29 5:47 ` Leon Romanovsky
2020-01-29 20:01 ` John Hubbard
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