From: Dan Williams <dan.j.williams@intel.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: david <david@fromorbit.com>, "Jérôme Glisse" <jglisse@redhat.com>,
"Jan Kara" <jack@suse.cz>, "Matthew Wilcox" <willy@infradead.org>,
"John Hubbard" <john.hubbard@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Linux MM" <linux-mm@kvack.org>,
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>,
"Dave Hansen" <dave.hansen@intel.com>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
Date: Fri, 14 Dec 2018 11:38:59 -0800 [thread overview]
Message-ID: <CAPcyv4hrbA9H20bi+QMpKNi7r=egstt61MdQSD5Fb293W1btaw@mail.gmail.com> (raw)
In-Reply-To: <01cf4e0c-b2d6-225a-3ee9-ef0f7e53684d@nvidia.com>
On Thu, Dec 13, 2018 at 10:11 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 12/13/18 9:21 PM, Dan Williams wrote:
> > On Thu, Dec 13, 2018 at 7:53 PM John Hubbard <jhubbard@nvidia.com> wrote:
> >>
> >> On 12/12/18 4:51 PM, Dave Chinner wrote:
> >>> On Wed, Dec 12, 2018 at 04:59:31PM -0500, Jerome Glisse wrote:
> >>>> On Thu, Dec 13, 2018 at 08:46:41AM +1100, Dave Chinner wrote:
> >>>>> On Wed, Dec 12, 2018 at 10:03:20AM -0500, Jerome Glisse wrote:
> >>>>>> On Mon, Dec 10, 2018 at 11:28:46AM +0100, Jan Kara wrote:
> >>>>>>> On Fri 07-12-18 21:24:46, Jerome Glisse wrote:
> >>>>>>> So this approach doesn't look like a win to me over using counter in struct
> >>>>>>> page and I'd rather try looking into squeezing HMM public page usage of
> >>>>>>> struct page so that we can fit that gup counter there as well. I know that
> >>>>>>> it may be easier said than done...
> >>>>>>
> >>
> >> Agreed. After all the discussion this week, I'm thinking that the original idea
> >> of a per-struct-page counter is better. Fortunately, we can do the moral equivalent
> >> of that, unless I'm overlooking something: Jerome had another proposal that he
> >> described, off-list, for doing that counting, and his idea avoids the problem of
> >> finding space in struct page. (And in fact, when I responded yesterday, I initially
> >> thought that's where he was going with this.)
> >>
> >> So how about this hybrid solution:
> >>
> >> 1. Stay with the basic RFC approach of using a per-page counter, but actually
> >> store the counter(s) in the mappings instead of the struct page. We can use
> >> !PageAnon and page_mapping to look up all the mappings, stash the dma_pinned_count
> >> there. So the total pinned count is scattered across mappings. Probably still need
> >> a PageDmaPinned bit.
> >
> > How do you safely look at page->mapping from the get_user_pages_fast()
> > path? You'll be racing invalidation disconnecting the page from the
> > mapping.
> >
>
> I don't have an answer for that, so maybe the page->mapping idea is dead already.
>
> So in that case, there is still one more way to do all of this, which is to
> combine ZONE_DEVICE, HMM, and gup/dma information in a per-page struct, and get
> there via basically page->private, more or less like this:
If we're going to allocate something new out-of-line then maybe we
should go even further to allow for a page "proxy" object to front a
real struct page. This idea arose from Dave Hansen as I explained to
him the dax-reflink problem, and dovetails with Dave Chinner's
suggestion earlier in this thread for dax-reflink.
Have get_user_pages() allocate a proxy object that gets passed around
to drivers. Something like a struct page pointer with bit 0 set. This
would add a conditional branch and pointer chase to many page
operations, like page_to_pfn(), I thought something like it would be
unacceptable a few years ago, but then HMM went and added similar
overhead to put_page() and nobody balked.
This has the additional benefit of catching cases that might be doing
a get_page() on a get_user_pages() result and should instead switch to
a "ref_user_page()" (opposite of put_user_page()) as the API to take
additional references on a get_user_pages() result.
page->index and page->mapping could be overridden by similar
attributes in the proxy, and allow an N:1 relationship of proxy
instances to actual pages. Filesystems could generate dynamic proxies
as well.
The auxiliary information (dev_pagemap, hmm_data, etc...) moves to the
proxy and stops polluting the base struct page which remains the
canonical location for dirty-tracking and dma operations.
The difficulties are reconciling the source of the proxies as both
get_user_pages() and filesystem may want to be the source of the
allocation. In the get_user_pages_fast() path we may not be able to
ask the filesystem for the proxy, at least not without destroying the
performance expectations of get_user_pages_fast().
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5ed8f6292a53..13f651bb5cc1 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -67,6 +67,13 @@ struct hmm;
> #define _struct_page_alignment
> #endif
>
> +struct page_aux {
> + struct dev_pagemap *pgmap;
> + unsigned long hmm_data;
> + unsigned long private;
> + atomic_t dma_pinned_count;
> +};
> +
> struct page {
> unsigned long flags; /* Atomic flags, some possibly
> * updated asynchronously */
> @@ -149,11 +156,13 @@ struct page {
> spinlock_t ptl;
> #endif
> };
> - struct { /* ZONE_DEVICE pages */
> + struct { /* ZONE_DEVICE, HMM or get_user_pages() pages */
> /** @pgmap: Points to the hosting device page map. */
> - struct dev_pagemap *pgmap;
> - unsigned long hmm_data;
> - unsigned long _zd_pad_1; /* uses mapping */
> + unsigned long _zd_pad_1; /* LRU */
> + unsigned long _zd_pad_2; /* LRU */
> + unsigned long _zd_pad_3; /* mapping */
> + unsigned long _zd_pad_4; /* index */
> + struct page_aux *aux; /* private */
> };
>
> /** @rcu_head: You can use this to free a page by RCU. */
>
> ...is there any appetite for that approach?
>
> --
> thanks,
> John Hubbard
> NVIDIA
next prev parent reply other threads:[~2018-12-14 19:38 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
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 [this message]
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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