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 [thread overview]
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.
next prev parent reply other threads:[~2018-12-07 19:26 UTC|newest]
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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