From: "Kirill A. Shutemov" <kirill@shutemov.name>
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>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Matthew Wilcox" <willy@infradead.org>,
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>
Subject: Re: [PATCH v3 08/12] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages
Date: Mon, 3 Feb 2020 16:45:29 +0300 [thread overview]
Message-ID: <20200203134529.onxociznb5mgtjhf@box> (raw)
In-Reply-To: <20200201034029.4063170-9-jhubbard@nvidia.com>
On Fri, Jan 31, 2020 at 07:40:25PM -0800, John Hubbard wrote:
> For huge pages (and in fact, any compound page), the
> GUP_PIN_COUNTING_BIAS scheme tends to overflow too easily, each tail
> page increments the head page->_refcount by GUP_PIN_COUNTING_BIAS
> (1024). That limits the number of huge pages that can be pinned.
>
> This patch removes that limitation, by using an exact form of pin
> counting for compound pages of order > 1. The "order > 1" is required
> because this approach uses the 3rd struct page in the compound page, and
> order 1 compound pages only have two pages, so that won't work there.
Could you update the comment for HPAGE_PMD_ORDER < 2 check in
hugepage_init() to reflect addtional user for the condition.
>
> A new struct page field, hpage_pinned_refcount, has been added,
> replacing a padding field in the union (so no new space is used).
>
> This enhancement also has a useful side effect: huge pages and compound
> pages (of order > 1) do not suffer from the "potential false positives"
> problem that is discussed in the page_dma_pinned() comment block. That
> is because these compound pages have extra space for tracking things, so
> they get exact pin counts instead of overloading page->_refcount.
>
> Documentation/core-api/pin_user_pages.rst is updated accordingly.
>
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-02-03 13:45 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-01 3:40 [PATCH v3 00/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-01 3:40 ` [PATCH v3 01/12] mm: dump_page(): better diagnostics for compound pages John Hubbard
2020-02-03 13:16 ` Kirill A. Shutemov
2020-02-03 19:51 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 02/12] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-02-03 13:17 ` Kirill A. Shutemov
2020-02-03 14:20 ` Jan Kara
2020-02-03 21:09 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 03/12] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-02-03 13:19 ` Kirill A. Shutemov
2020-02-03 19:56 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 04/12] mm: introduce page_ref_sub_return() John Hubbard
2020-02-03 13:23 ` Kirill A. Shutemov
2020-02-03 20:03 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 05/12] mm/gup: pass gup flags to two more routines John Hubbard
2020-02-03 13:24 ` Kirill A. Shutemov
2020-02-03 14:18 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 06/12] mm/gup: require FOLL_GET for get_user_pages_fast() John Hubbard
2020-02-03 13:26 ` Kirill A. Shutemov
2020-02-03 14:18 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 07/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-03 13:40 ` Kirill A. Shutemov
2020-02-03 21:01 ` John Hubbard
2020-02-03 14:29 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 08/12] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-02-03 13:45 ` Kirill A. Shutemov [this message]
2020-02-03 14:43 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 09/12] mm: dump_page(): better diagnostics for huge pinned pages John Hubbard
2020-02-03 13:46 ` Kirill A. Shutemov
2020-02-03 14:44 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-02-03 13:53 ` Kirill A. Shutemov
2020-02-03 21:04 ` John Hubbard
2020-02-03 21:30 ` Kirill A. Shutemov
2020-02-03 21:34 ` John Hubbard
2020-02-03 23:16 ` John Hubbard
2020-02-03 23:43 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 11/12] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-02-03 13:58 ` Kirill A. Shutemov
2020-02-03 21:17 ` John Hubbard
2020-02-03 21:55 ` Kirill A. Shutemov
2020-02-03 22:07 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 12/12] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200203134529.onxociznb5mgtjhf@box \
--to=kirill@shutemov.name \
--cc=akpm@linux-foundation.org \
--cc=corbet@lwn.net \
--cc=dan.j.williams@intel.com \
--cc=david@fromorbit.com \
--cc=hch@infradead.org \
--cc=ira.weiny@intel.com \
--cc=jack@suse.cz \
--cc=jgg@ziepe.ca \
--cc=jglisse@redhat.com \
--cc=jhubbard@nvidia.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-rdma@vger.kernel.org \
--cc=mhocko@suse.com \
--cc=mike.kravetz@oracle.com \
--cc=shuah@kernel.org \
--cc=vbabka@suse.cz \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).