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From: Jerome Glisse <jglisse@redhat.com>
To: Boaz Harrosh <openosd@gmail.com>
Cc: "Boaz Harrosh" <boaz@plexistor.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Kent Overstreet" <kent.overstreet@gmail.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-block@vger.kernel.org, "Linux MM" <linux-mm@kvack.org>,
	"John Hubbard" <jhubbard@nvidia.com>, "Jan Kara" <jack@suse.cz>,
	"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, "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>,
	"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 19:34:03 -0400	[thread overview]
Message-ID: <20190416233402.GC22465@redhat.com> (raw)
In-Reply-To: <41e2d7e1-104b-a006-2824-015ca8c76cc8@gmail.com>

On Wed, Apr 17, 2019 at 01:09:22AM +0300, Boaz Harrosh wrote:
> On 16/04/19 22:57, Jerome Glisse wrote:
> <>
> > 
> > A very long thread on this:
> > 
> > https://lkml.org/lkml/2018/12/3/1128
> > 
> > especialy all the reply to this first one
> > 
> > There is also:
> > 
> > https://lkml.org/lkml/2019/3/26/1395
> > https://lwn.net/Articles/753027/
> > 
> 
> OK I have re-read this patchset and a little bit of the threads above (not all)
> 
> As I understand the long term plan is to keep two separate ref-counts one
> for GUP-ref and one for the regular page-state/ownership ref.
> Currently looking at page-ref we do not know if we have a GUP currently held.
> With the new plan we can (Still not sure what's the full plan with this new info)
> 
> But if you make it such as the first GUP-ref also takes a page_ref and the
> last GUp-dec also does put_page. Then the all of these becomes a matter of
> matching every call to get_user_pages or iov_iter_get_pages() with a new
> put_user_pages or iov_iter_put_pages().

So sorry forgot to answer that part. So idea is to do:
    GUP() {
        ...
-       page_ref_inc(page);
+       page_ref_add(page, GUP_BIAS);
        ...
    }

with GUP_BIAS = 1024 or something big but not too big to avoid risk of
overflow by GUP. Then put_user_page() just ref_sub instead of ref_dec
the same amount.

We can have false GUP positive if a page is map so many time or reference
so many time that its refcount reach the GUP_BIAS value but considering
such page as GUPed should not be too harmful (not more harmful than what
we do with GUPed page).

So we want to call put_user_page() for GUPed page and only GUPed page so
that we keep the reference count properly balance.

Cheers,
Jérôme

  parent reply	other threads:[~2019-04-16 23:34 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
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 [this message]
2019-04-17 21:54         ` Dan Williams

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