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From: Dan Williams <dan.j.williams@intel.com>
To: "Jérôme Glisse" <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>,
	Matthew Wilcox <willy@infradead.org>,
	John Hubbard <john.hubbard@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux MM <linux-mm@kvack.org>, Jan Kara <jack@suse.cz>,
	tom@talpey.com, Al Viro <viro@zeniv.linux.org.uk>,
	benve@cisco.com, Christoph Hellwig <hch@infradead.org>,
	Christopher Lameter <cl@linux.com>,
	"Dalessandro, Dennis" <dennis.dalessandro@intel.com>,
	Doug Ledford <dledford@redhat.com>,
	Jason Gunthorpe <jgg@ziepe.ca>, Michal Hocko <mhocko@kernel.org>,
	Mike Marciniszyn <mike.marciniszyn@intel.com>,
	rcampbell@nvidia.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
Date: Fri, 7 Dec 2018 11:26:34 -0800
Message-ID: <CAPcyv4ig0Lg+6Abc+P9guOSdszk0B4LyHGh=wXf_kMzGs=5oww@mail.gmail.com> (raw)
In-Reply-To: <20181207191620.GD3293@redhat.com>

On Fri, Dec 7, 2018 at 11:16 AM Jerome Glisse <jglisse@redhat.com> wrote:
>
> On Thu, Dec 06, 2018 at 06:45:49PM -0800, John Hubbard wrote:
> > On 12/4/18 5:57 PM, John Hubbard wrote:
> > > On 12/4/18 5:44 PM, Jerome Glisse wrote:
> > >> On Tue, Dec 04, 2018 at 05:15:19PM -0800, Matthew Wilcox wrote:
> > >>> On Tue, Dec 04, 2018 at 04:58:01PM -0800, John Hubbard wrote:
> > >>>> On 12/4/18 3:03 PM, Dan Williams wrote:
> > >>>>> Except the LRU fields are already in use for ZONE_DEVICE pages... how
> > >>>>> does this proposal interact with those?
> > >>>>
> > >>>> Very badly: page->pgmap and page->hmm_data both get corrupted. Is there an entire
> > >>>> use case I'm missing: calling get_user_pages() on ZONE_DEVICE pages? Said another
> > >>>> way: is it reasonable to disallow calling get_user_pages() on ZONE_DEVICE pages?
> > >>>>
> > >>>> If we have to support get_user_pages() on ZONE_DEVICE pages, then the whole
> > >>>> LRU field approach is unusable.
> > >>>
> > >>> We just need to rearrange ZONE_DEVICE pages.  Please excuse the whitespace
> > >>> damage:
> > >>>
> > >>> +++ b/include/linux/mm_types.h
> > >>> @@ -151,10 +151,12 @@ struct page {
> > >>>  #endif
> > >>>                 };
> > >>>                 struct {        /* ZONE_DEVICE pages */
> > >>> +                       unsigned long _zd_pad_2;        /* LRU */
> > >>> +                       unsigned long _zd_pad_3;        /* LRU */
> > >>> +                       unsigned long _zd_pad_1;        /* uses mapping */
> > >>>                         /** @pgmap: Points to the hosting device page map. */
> > >>>                         struct dev_pagemap *pgmap;
> > >>>                         unsigned long hmm_data;
> > >>> -                       unsigned long _zd_pad_1;        /* uses mapping */
> > >>>                 };
> > >>>
> > >>>                 /** @rcu_head: You can use this to free a page by RCU. */
> > >>>
> > >>> You don't use page->private or page->index, do you Dan?
> > >>
> > >> page->private and page->index are use by HMM DEVICE page.
> > >>
> > >
> > > OK, so for the ZONE_DEVICE + HMM case, that leaves just one field remaining for
> > > dma-pinned information. Which might work. To recap, we need:
> > >
> > > -- 1 bit for PageDmaPinned
> > > -- 1 bit, if using LRU field(s), for PageDmaPinnedWasLru.
> > > -- N bits for a reference count
> > >
> > > Those *could* be packed into a single 64-bit field, if really necessary.
> > >
> >
> > ...actually, this needs to work on 32-bit systems, as well. And HMM is using a lot.
> > However, it is still possible for this to work.
> >
> > Matthew, can I have that bit now please? I'm about out of options, and now it will actually
> > solve the problem here.
> >
> > Given:
> >
> > 1) It's cheap to know if a page is ZONE_DEVICE, and ZONE_DEVICE means not on the LRU.
> > That, in turn, means only 1 bit instead of 2 bits (in addition to a counter) is required,
> > for that case.
> >
> > 2) There is an independent bit available (according to Matthew).
> >
> > 3) HMM uses 4 of the 5 struct page fields, so only one field is available for a counter
> >    in that case.
>
> To expend on this, HMM private page are use for anonymous page
> so the index and mapping fields have the value you expect for
> such pages. Down the road i want also to support file backed
> page with HMM private (mapping, private, index).
>
> For HMM public both anonymous and file back page are supported
> today (HMM public is only useful on platform with something like
> OpenCAPI, CCIX or NVlink ... so PowerPC for now).
>
> > 4) get_user_pages() must work on ZONE_DEVICE and HMM pages.
>
> get_user_pages() only need to work with HMM public page not the
> private one as we can not allow _anyone_ to pin HMM private page.

How does HMM enforce that? Because the kernel should not allow *any*
memory management facility to arbitrarily fail direct-I/O operations.
That's why CONFIG_FS_DAX_LIMITED is a temporary / experimental hack
for S390 and ZONE_DEVICE was invented to bypass that hack for X86 and
any arch that plans to properly support DAX. I would classify any
memory management that can't support direct-I/O in the same
"experimental" category.

  reply index

Thread overview: 213+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-04  0:17 [PATCH 0/2] put_user_page*(): start converting the call sites john.hubbard
2018-12-04  0:17 ` [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions john.hubbard
2018-12-04  7:53   ` Mike Rapoport
2018-12-05  1:40     ` John Hubbard
2018-12-04 20:28   ` Dan Williams
2018-12-04 21:56     ` John Hubbard
2018-12-04 23:03       ` Dan Williams
2018-12-05  0:36         ` Jerome Glisse
2018-12-05  0:40           ` Dan Williams
2018-12-05  0:59             ` John Hubbard
2018-12-05  0:58         ` John Hubbard
2018-12-05  1:00           ` Dan Williams
2018-12-05  1:15           ` Matthew Wilcox
2018-12-05  1:44             ` Jerome Glisse
2018-12-05  1:57               ` John Hubbard
2018-12-07  2:45                 ` John Hubbard
2018-12-07 19:16                   ` Jerome Glisse
2018-12-07 19:26                     ` Dan Williams [this message]
2018-12-07 19:40                       ` Jerome Glisse
2018-12-08  0:52                     ` John Hubbard
2018-12-08  2:24                       ` Jerome Glisse
2018-12-10 10:28                         ` Jan Kara
2018-12-12 15:03                           ` Jerome Glisse
2018-12-12 16:27                             ` Dan Williams
2018-12-12 17:02                               ` Jerome Glisse
2018-12-12 17:49                                 ` Dan Williams
2018-12-12 19:07                                   ` John Hubbard
2018-12-12 21:30                               ` Jerome Glisse
2018-12-12 21:40                                 ` Dan Williams
2018-12-12 21:53                                   ` Jerome Glisse
2018-12-12 22:11                                     ` Matthew Wilcox
2018-12-12 22:16                                       ` Jerome Glisse
2018-12-12 23:37                                     ` Jason Gunthorpe
2018-12-12 23:46                                       ` John Hubbard
2018-12-12 23:54                                       ` Dan Williams
2018-12-13  0:01                                       ` Jerome Glisse
2018-12-13  0:18                                         ` Dan Williams
2018-12-13  0:44                                           ` Jerome Glisse
2018-12-13  3:26                                             ` Jason Gunthorpe
2018-12-13  3:20                                         ` Jason Gunthorpe
2018-12-13 12:43                                           ` Jerome Glisse
2018-12-13 13:40                                             ` Tom Talpey
2018-12-13 14:18                                               ` Jerome Glisse
2018-12-13 14:51                                                 ` Tom Talpey
2018-12-13 15:18                                                   ` Jerome Glisse
2018-12-13 18:12                                                     ` Tom Talpey
2018-12-13 19:18                                                       ` Jerome Glisse
2018-12-14 10:41                                             ` Jan Kara
2018-12-14 15:25                                               ` Jerome Glisse
2018-12-12 21:56                                 ` John Hubbard
2018-12-12 22:04                                   ` Jerome Glisse
2018-12-12 22:11                                     ` John Hubbard
2018-12-12 22:14                                       ` Jerome Glisse
2018-12-12 22:17                                         ` John Hubbard
2018-12-12 21:46                             ` Dave Chinner
2018-12-12 21:59                               ` Jerome Glisse
2018-12-13  0:51                                 ` Dave Chinner
2018-12-13  2:02                                   ` Jerome Glisse
2018-12-13 15:56                                     ` Christopher Lameter
2018-12-13 16:02                                       ` Jerome Glisse
2018-12-14  6:00                                     ` Dave Chinner
2018-12-14 15:13                                       ` Jerome Glisse
2018-12-14  3:52                                   ` John Hubbard
2018-12-14  5:21                                     ` Dan Williams
2018-12-14  6:11                                       ` John Hubbard
2018-12-14 15:20                                         ` Jerome Glisse
2018-12-14 19:38                                         ` Dan Williams
2018-12-14 19:48                                           ` Matthew Wilcox
2018-12-14 19:53                                             ` Dave Hansen
2018-12-14 20:03                                               ` Matthew Wilcox
2018-12-14 20:17                                                 ` Dan Williams
2018-12-14 20:29                                                   ` Matthew Wilcox
2018-12-15  0:41                                                 ` John Hubbard
2018-12-17  8:56                                           ` Jan Kara
2018-12-17 18:28                                             ` Dan Williams
2018-12-14 15:43                               ` Jan Kara
2018-12-16 21:58                                 ` Dave Chinner
2018-12-17 18:11                                   ` Jerome Glisse
2018-12-17 18:34                                     ` Matthew Wilcox
2018-12-17 19:48                                       ` Jerome Glisse
2018-12-17 19:51                                         ` Matthew Wilcox
2018-12-17 19:54                                           ` Jerome Glisse
2018-12-17 19:59                                             ` Matthew Wilcox
2018-12-17 20:55                                               ` Jerome Glisse
2018-12-17 21:03                                                 ` Matthew Wilcox
2018-12-17 21:15                                                   ` Jerome Glisse
2018-12-18  1:09                                       ` Dave Chinner
2018-12-18  6:12                                       ` Darrick J. Wong
2018-12-18  9:30                                       ` Jan Kara
2018-12-18 23:29                                         ` John Hubbard
2018-12-19  2:07                                           ` Jerome Glisse
2018-12-19 11:08                                             ` Jan Kara
2018-12-20 10:54                                               ` John Hubbard
2018-12-20 16:50                                                 ` Jerome Glisse
2018-12-20 16:57                                                   ` Dan Williams
2018-12-20 16:49                                               ` Jerome Glisse
2019-01-03  1:55                                               ` Jerome Glisse
2019-01-03  3:27                                                 ` John Hubbard
2019-01-03 14:57                                                   ` Jerome Glisse
2019-01-03  9:26                                                 ` Jan Kara
2019-01-03 14:44                                                   ` Jerome Glisse
2019-01-11  2:59                                                     ` John Hubbard
2019-01-11  2:59                                                       ` John Hubbard
2019-01-11 16:51                                                       ` Jerome Glisse
2019-01-11 16:51                                                         ` Jerome Glisse
2019-01-12  1:04                                                         ` John Hubbard
2019-01-12  1:04                                                           ` John Hubbard
2019-01-12  2:02                                                           ` Jerome Glisse
2019-01-12  2:02                                                             ` Jerome Glisse
2019-01-12  2:38                                                             ` John Hubbard
2019-01-12  2:38                                                               ` John Hubbard
2019-01-12  2:46                                                               ` Jerome Glisse
2019-01-12  2:46                                                                 ` Jerome Glisse
2019-01-12  3:06                                                                 ` John Hubbard
2019-01-12  3:06                                                                   ` John Hubbard
2019-01-12  3:25                                                                   ` Jerome Glisse
2019-01-12  3:25                                                                     ` Jerome Glisse
2019-01-12 20:46                                                                     ` John Hubbard
2019-01-12 20:46                                                                       ` John Hubbard
2019-01-14 14:54                                                                   ` Jan Kara
2019-01-14 14:54                                                                     ` Jan Kara
2019-01-14 17:21                                                                     ` Jerome Glisse
2019-01-14 17:21                                                                       ` Jerome Glisse
2019-01-14 19:09                                                                       ` John Hubbard
2019-01-14 19:09                                                                         ` John Hubbard
2019-01-15  8:34                                                                         ` Jan Kara
2019-01-15  8:34                                                                           ` Jan Kara
2019-01-15 21:39                                                                           ` John Hubbard
2019-01-15 21:39                                                                             ` John Hubbard
2019-01-15  8:07                                                                       ` Jan Kara
2019-01-15  8:07                                                                         ` Jan Kara
2019-01-15 17:15                                                                         ` Jerome Glisse
2019-01-15 17:15                                                                           ` Jerome Glisse
2019-01-15 21:56                                                                           ` John Hubbard
2019-01-15 21:56                                                                             ` John Hubbard
2019-01-15 22:12                                                                             ` Jerome Glisse
2019-01-15 22:12                                                                               ` Jerome Glisse
2019-01-16  0:44                                                                               ` John Hubbard
2019-01-16  0:44                                                                                 ` John Hubbard
2019-01-16  1:56                                                                                 ` Jerome Glisse
2019-01-16  1:56                                                                                   ` Jerome Glisse
2019-01-16  2:01                                                                                   ` Dan Williams
2019-01-16  2:01                                                                                     ` Dan Williams
2019-01-16  2:23                                                                                     ` Jerome Glisse
2019-01-16  2:23                                                                                       ` Jerome Glisse
2019-01-16  4:34                                                                                       ` Dave Chinner
2019-01-16  4:34                                                                                         ` Dave Chinner
2019-01-16 14:50                                                                                         ` Jerome Glisse
2019-01-16 14:50                                                                                           ` Jerome Glisse
2019-01-16 22:51                                                                                           ` Dave Chinner
2019-01-16 22:51                                                                                             ` Dave Chinner
2019-01-16 11:38                                                                         ` Jan Kara
2019-01-16 11:38                                                                           ` Jan Kara
2019-01-16 13:08                                                                           ` Jerome Glisse
2019-01-16 13:08                                                                             ` Jerome Glisse
2019-01-17  5:42                                                                             ` John Hubbard
2019-01-17  5:42                                                                               ` John Hubbard
2019-01-17 15:21                                                                               ` Jerome Glisse
2019-01-17 15:21                                                                                 ` Jerome Glisse
2019-01-18  0:16                                                                                 ` Dave Chinner
2019-01-18  1:59                                                                                   ` Jerome Glisse
2019-01-17  9:30                                                                             ` Jan Kara
2019-01-17  9:30                                                                               ` Jan Kara
2019-01-17 15:17                                                                               ` Jerome Glisse
2019-01-17 15:17                                                                                 ` Jerome Glisse
2019-01-22 15:24                                                                                 ` Jan Kara
2019-01-22 16:46                                                                                   ` Jerome Glisse
2019-01-23 18:02                                                                                     ` Jan Kara
2019-01-23 19:04                                                                                       ` Jerome Glisse
2019-01-29  0:22                                                                                         ` John Hubbard
2019-01-29  1:23                                                                                           ` Jerome Glisse
2019-01-29  6:41                                                                                             ` John Hubbard
2019-01-29 10:12                                                                                               ` Jan Kara
2019-01-30  2:21                                                                                                 ` John Hubbard
2019-01-17  5:25                                                                         ` John Hubbard
2019-01-17  5:25                                                                           ` John Hubbard
2019-01-17  9:04                                                                           ` Jan Kara
2019-01-17  9:04                                                                             ` Jan Kara
2019-01-12  3:14                                                               ` Jerome Glisse
2019-01-12  3:14                                                                 ` Jerome Glisse
2018-12-18 10:33                                   ` Jan Kara
2018-12-18 23:42                                     ` Dave Chinner
2018-12-19  3:03                                       ` Jason Gunthorpe
2018-12-19  5:26                                         ` Dan Williams
2018-12-19 11:19                                           ` Jan Kara
2018-12-19 10:28                                         ` Dave Chinner
2018-12-19 11:35                                           ` Jan Kara
2018-12-19 16:56                                             ` Jason Gunthorpe
2018-12-19 22:33                                             ` Dave Chinner
2018-12-20  9:07                                               ` Jan Kara
2018-12-20 16:54                                               ` Jerome Glisse
2018-12-19 13:24                                       ` Jan Kara
2018-12-08  5:18                       ` Matthew Wilcox
2018-12-12 19:13                         ` John Hubbard
2018-12-08  7:16                       ` Dan Williams
2018-12-08 16:33                         ` Jerome Glisse
2018-12-08 16:48                           ` Christoph Hellwig
2018-12-08 17:47                             ` Jerome Glisse
2018-12-08 18:26                               ` Christoph Hellwig
2018-12-08 18:45                                 ` Jerome Glisse
2018-12-08 18:09                             ` Dan Williams
2018-12-08 18:12                               ` Christoph Hellwig
2018-12-11  6:18                               ` Dave Chinner
2018-12-05  5:52             ` Dan Williams
2018-12-05 11:16       ` Jan Kara
2018-12-04  0:17 ` [PATCH 2/2] infiniband/mm: convert put_page() to put_user_page*() john.hubbard
2018-12-04 17:10 ` [PATCH 0/2] put_user_page*(): start converting the call sites David Laight
2018-12-05  1:05   ` John Hubbard
2018-12-05 14:08     ` David Laight
2018-12-28  8:37       ` Pavel Machek
2019-02-08  7:56 [PATCH 0/2] mm: put_user_page() call site conversion first john.hubbard
2019-02-08  7:56 ` [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions john.hubbard
2019-02-08 10:32   ` Mike Rapoport
2019-02-08 20:44     ` John Hubbard

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