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From: Kent Overstreet <kent.overstreet@gmail.com>
To: Boaz Harrosh <boaz@plexistor.com>
Cc: jglisse@redhat.com, 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>,
	"Steve French" <sfrench@samba.org>,
	linux-cifs@vger.kernel.org, samba-technical@lists.samba.org,
	"Yan Zheng" <zyan@redhat.com>, "Sage Weil" <sage@redhat.com>,
	"Ilya Dryomov" <idryomov@gmail.com>,
	"Alex Elder" <elder@kernel.org>,
	ceph-devel@vger.kernel.org,
	"Eric Van Hensbergen" <ericvh@gmail.com>,
	"Latchesar Ionkov" <lucho@ionkov.net>,
	"Mike Marshall" <hubcap@omnibond.com>,
	"Martin Brandenburg" <martin@omnibond.com>,
	devel@lists.orangefs.org,
	"Dominique Martinet" <asmadeus@codewreck.org>,
	v9fs-developer@lists.sourceforge.net, "Coly Li" <colyli@suse.de>,
	linux-bcache@vger.kernel.org,
	"Ernesto A. Fernández" <ernesto.mnd.fernandez@gmail.com>
Subject: Re: [PATCH v1 00/15] Keep track of GUPed pages in fs and block
Date: Tue, 16 Apr 2019 14:59:22 -0400	[thread overview]
Message-ID: <20190416185922.GA12818@kmo-pixel> (raw)
In-Reply-To: <2c124cc4-b97e-ee28-2926-305bc6bc74bd@plexistor.com>

On Tue, Apr 16, 2019 at 09:35:04PM +0300, Boaz Harrosh wrote:
> On Thu, Apr 11, 2019 at 05:08:19PM -0400, jglisse@redhat.com wrote:
> > From: Jérôme Glisse <jglisse@redhat.com>
> > 
> > This patchset depends on various small fixes [1] and also on patchset
> > which introduce put_user_page*() [2] and thus is 5.3 material as those
> > pre-requisite will get in 5.2 at best. Nonetheless i am posting it now
> > so that it can get review and comments on how and what should be done
> > to test things.
> > 
> > For various reasons [2] [3] we want to track page reference through GUP
> > differently than "regular" page reference. Thus we need to keep track
> > of how we got a page within the block and fs layer. To do so this patch-
> > set change the bio_bvec struct to store a pfn and flags instead of a
> > direct pointer to a page. This way we can flag page that are coming from
> > GUP.
> > 
> > This patchset is divided as follow:
> >     - First part of the patchset is just small cleanup i believe they
> >       can go in as his assuming people are ok with them.
> 
> 
> >     - Second part convert bio_vec->bv_page to bio_vec->bv_pfn this is
> >       done in multi-step, first we replace all direct dereference of
> >       the field by call to inline helper, then we introduce macro for
> >       bio_bvec that are initialized on the stack. Finaly we change the
> >       bv_page field to bv_pfn.
> 
> Why do we need a bv_pfn. Why not just use the lowest bit of the page-ptr
> as a flag (pointer always aligned to 64 bytes in our case).
> 
> So yes we need an inline helper for reference of the page but is it not clearer
> that we assume a page* and not any kind of pfn ?
> It will not be the first place using low bits of a pointer for flags.
> 
> That said. Why we need it at all? I mean why not have it as a bio flag. If it exist
> at all that a user has a GUP and none-GUP pages to IO at the same request he/she
> can just submit them as two separate BIOs (chained at the block layer).
> 
> Many users just submit one page bios and let elevator merge them any way.

Let's please not add additional flags and weirdness to struct bio - "if this
flag is set interpret one way, if not interpret another" - or eventually bios
will be as bad as skbuffs. I would much prefer just changing bv_page to bv_pfn.

Question though - why do we need a flag for whether a page is a GUP page or not?
Couldn't the needed information just be determined by what range the pfn is not
(i.e. whether or not it has a struct page associated with it)?

  parent reply	other threads:[~2019-04-16 18:59 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
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 [this message]
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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