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From: Jerome Glisse <jglisse@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, linux-mm@kvack.org,
	"John Hubbard" <jhubbard@nvidia.com>, "Jan Kara" <jack@suse.cz>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Johannes Thumshirn" <jthumshirn@suse.de>,
	"Christoph Hellwig" <hch@lst.de>, "Jens Axboe" <axboe@kernel.dk>,
	"Ming Lei" <ming.lei@redhat.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Ernesto A . Fernández" <ernesto.mnd.fernandez@gmail.com>,
	"Jeff Moyer" <jmoyer@redhat.com>
Subject: Re: [PATCH v1 12/15] fs/direct-io: keep track of wether a page is coming from GUP or not
Date: Thu, 11 Apr 2019 20:08:46 -0400	[thread overview]
Message-ID: <20190412000846.GB13369@redhat.com> (raw)
In-Reply-To: <20190411231443.GD1695@dread.disaster.area>

On Fri, Apr 12, 2019 at 09:14:43AM +1000, Dave Chinner wrote:
> On Thu, Apr 11, 2019 at 05:08:31PM -0400, jglisse@redhat.com wrote:
> > From: Jérôme Glisse <jglisse@redhat.com>
> > 
> > We want to keep track of how we got a reference on page when doing DIO,
> > ie wether the page was reference through GUP (get_user_page*) or not.
> > For that this patch rework the way page reference is taken and handed
> > over between DIO code and BIO. Instead of taking a reference for page
> > that have been successfuly added to a BIO we just steal the reference
> > we have when we lookup the page (either through GUP or for ZERO_PAGE).
> > 
> > So this patch keep track of wether the reference has been stolen by the
> > BIO or not. This avoids a bunch of get_page()/put_page() so this limit
> > the number of atomic operations.
> 
> Is the asme set of changes appropriate for the fs/iomap.c direct IO
> path (i.e. XFS)?

Yes and it is part of this patchset AFAICT iomap use bio_iov_iter_get_pages()
which is updated to pass down wether page are coming from GUP or not. The
bio you get out of that is then release through iomap_dio_bio_end_io() which
calls bvec_put_page() which will use put_user_page() for GUPed page.

I may have miss a case and review are welcome.

Note that while the convertion is happening put_user_page is exactly the same
as put_page() in fact the implementation just call put_page() with nothing
else.

The tricky part is making sure that before we diverge with a put_user_page()
that does something else that put_page() we will need to be sure that we did
not left a path that do GUP but does call put_page() and not put_user_page().
We have some plan to catch that in debug build.

In any case i believe we will be very careful when the times come to change
put_user_page() to something different.

Cheers,
Jérôme

  reply	other threads:[~2019-04-12  0:08 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-11 21:08 [PATCH v1 00/15] Keep track of GUPed pages in fs and block jglisse
2019-04-11 21:08 ` [PATCH v1 01/15] fs/direct-io: fix trailing whitespace issues jglisse
2019-04-11 21:08 ` [PATCH v1 02/15] iov_iter: add helper to test if an iter would use GUP jglisse
2019-04-11 21:08 ` [PATCH v1 03/15] block: introduce bvec_page()/bvec_set_page() to get/set bio_vec.bv_page jglisse
2019-04-11 21:08 ` [PATCH v1 04/15] block: introduce BIO_VEC_INIT() macro to initialize bio_vec structure jglisse
2019-04-11 21:08 ` [PATCH v1 05/15] block: replace all bio_vec->bv_page by bvec_page()/bvec_set_page() jglisse
2019-04-11 21:08 ` [PATCH v1 06/15] block: convert bio_vec.bv_page to bv_pfn to store pfn and not page jglisse
2019-04-11 21:08 ` [PATCH v1 07/15] block: add bvec_put_page_dirty*() to replace put_page(bvec_page()) jglisse
2019-04-11 21:08 ` [PATCH v1 08/15] block: use bvec_put_page() instead of put_page(bvec_page()) jglisse
2019-04-11 21:08 ` [PATCH v1 09/15] block: bvec_put_page_dirty* instead of set_page_dirty* and bvec_put_page jglisse
2019-04-11 21:08 ` [PATCH v1 10/15] block: add gup flag to bio_add_page()/bio_add_pc_page()/__bio_add_page() jglisse
2019-04-15 14:59   ` Jan Kara
2019-04-15 15:24     ` Jerome Glisse
2019-04-16 16:46       ` Jan Kara
2019-04-16 16:54         ` Dan Williams
2019-04-16 17:07         ` Jerome Glisse
2019-04-16  0:22     ` Jerome Glisse
2019-04-16 16:52       ` Jan Kara
2019-04-16 18:32         ` Jerome Glisse
2019-04-11 21:08 ` [PATCH v1 11/15] block: make sure bio_add_page*() knows page that are coming from GUP jglisse
2019-04-11 21:08 ` [PATCH v1 12/15] fs/direct-io: keep track of wether a page is coming from GUP or not jglisse
2019-04-11 23:14   ` Dave Chinner
2019-04-12  0:08     ` Jerome Glisse [this message]
2019-04-11 21:08 ` [PATCH v1 13/15] fs/splice: use put_user_page() when appropriate jglisse
2019-04-11 21:08 ` [PATCH v1 14/15] fs: use bvec_set_gup_page() where appropriate jglisse
2019-04-11 21:08 ` [PATCH v1 15/15] ceph: use put_user_pages() instead of ceph_put_page_vector() jglisse
2019-04-15  7:46   ` Yan, Zheng
2019-04-15 15:11     ` Jerome Glisse
2019-04-16  0:00 ` [PATCH v1 00/15] Keep track of GUPed pages in fs and block Dave Chinner
     [not found] ` <2c124cc4-b97e-ee28-2926-305bc6bc74bd@plexistor.com>
2019-04-16 18:47   ` Jerome Glisse
2019-04-16 18:59   ` Kent Overstreet
2019-04-16 19:12     ` Dan Williams
2019-04-16 19:49       ` Jerome Glisse
2019-04-17 21:53         ` Dan Williams
2019-04-17 22:28           ` Jerome Glisse
2019-04-17 23:32             ` Dan Williams
2019-04-18 10:42             ` Jan Kara
2019-04-18 14:27               ` Jerome Glisse
2019-04-18 15:30                 ` Jan Kara
2019-04-18 15:36                   ` Jerome Glisse
2019-04-18 18:03               ` Dan Williams
     [not found]       ` <ccac6c5a-7120-0455-88de-ca321b01e825@plexistor.com>
2019-04-16 19:57         ` Jerome Glisse
     [not found]           ` <41e2d7e1-104b-a006-2824-015ca8c76cc8@gmail.com>
2019-04-16 23:16             ` Jerome Glisse
     [not found]               ` <fa00a2ff-3664-3165-7af8-9d9c53238245@plexistor.com>
2019-04-17  2:03                 ` Jerome Glisse
2019-04-17 21:19                   ` Jerome Glisse
2019-04-16 23:34             ` Jerome Glisse
2019-04-17 21:54         ` Dan Williams

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