From: Jan Kara <jack@suse.cz>
To: lsf-pc@lists.linux-foundation.org
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
Dan Williams <dan.j.williams@intel.com>,
Jerome Glisse <jglisse@redhat.com>,
John Hubbard <jhubbard@nvidia.com>
Subject: [LSF/MM TOPIC] get_user_pages() pins in file mappings
Date: Thu, 24 Jan 2019 10:04:00 +0100 [thread overview]
Message-ID: <20190124090400.GE12184@quack2.suse.cz> (raw)
This is a joint proposal with Dan Williams, John Hubbard, and Jérôme
Glisse.
Last year we've talked with Dan about issues we have with filesystems and
GUP [1]. The crux of the problem lies in the fact that there is no
coordination (or even awareness) between filesystem working on a page (such
as doing writeback) and GUP user modifying page contents and setting it
dirty. This can (and we have user reports of this) lead to data corruption,
kernel crashes, and other fun.
Since last year we have worked together on solving these problems and we
have explored couple dead ends as well as hopefully found solutions to some
of the partial problems. So I'd like to give some overview of where we
stand and what remains to be solved and get thoughts from wider community
about proposed solutions / problems to be solved.
In particular we hope to have reasonably robust mechanism of identifying
pages pinned by GUP (patches will be posted soon) - I'd like to run that by
MM folks (unless discussion happens on mailing lists before LSF/MM). We
also have ideas how filesystems should react to pinned page in their
writepages methods - there will be some changes needed in some filesystems
to bounce the page if they need stable page contents. So I'd like to
explain why we chose to do bouncing to fs people (i.e., why we cannot just
wait, skip the page, do something else etc.) to save us from the same
discussion with each fs separately and also hash out what the API for
filesystems to do this should look like. Finally we plan to keep pinned
page permanently dirty - again something I'd like to explain why we do this
and gather input from other people.
This should be ideally shared MM + FS session.
[1] https://lwn.net/Articles/753027/
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next reply other threads:[~2019-01-24 9:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 9:04 Jan Kara [this message]
2019-01-26 2:58 ` [LSF/MM TOPIC] get_user_pages() pins in file mappings John Hubbard
2019-02-04 23:46 ` John Hubbard
2019-02-05 11:21 ` Jan Kara
2019-02-06 2:10 ` John Hubbard
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