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From: Dan Williams <dan.j.williams@intel.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Linux MM <linux-mm@kvack.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Matthew Wilcox <willy@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages
Date: Tue, 23 Feb 2021 10:18:30 -0800	[thread overview]
Message-ID: <CAPcyv4ixBjf7w-FtSaVOHoXccVag=gw7-mmaMYReV92pczy2tA@mail.gmail.com> (raw)
In-Reply-To: <e9e24d05-79e7-275a-530d-fc3b5041845d@oracle.com>

On Tue, Feb 23, 2021 at 9:19 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> On 2/23/21 4:50 PM, Dan Williams wrote:
> > On Tue, Feb 23, 2021 at 7:46 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >> On 2/22/21 8:37 PM, Dan Williams wrote:
> >>> On Mon, Feb 22, 2021 at 3:24 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >>>> On 2/20/21 1:43 AM, Dan Williams wrote:
> >>>>> On Tue, Dec 8, 2020 at 9:59 PM John Hubbard <jhubbard@nvidia.com> wrote:
> >>>>>> On 12/8/20 9:28 AM, Joao Martins wrote:
>
> [...]
>
> >>> Don't get me wrong the
> >>> capability is still needed for filesystem-dax, but the distinction is
> >>> that vmemmap_populate_compound_pages() need never worry about an
> >>> altmap.
> >>>
> >> IMO there's not much added complexity strictly speaking about altmap. We still use the
> >> same vmemmap_{pmd,pte,pgd}_populate helpers which just pass an altmap. So whatever it is
> >> being maintained for fsdax or other altmap consumers (e.g. we seem to be working towards
> >> hotplug making use of it) we are using it in the exact same way.
> >>
> >> The complexity of the future vmemmap_populate_compound_pages() has more to do with reusing
> >> vmemmap blocks allocated in previous vmemmap pages, and preserving that across section
> >> onlining (for 1G pages).
> >
> > True, I'm less worried about the complexity as much as
> > opportunistically converting configurations to RAM backed pages. It's
> > already the case that poison handling is page mapping size aligned for
> > device-dax, and filesystem-dax needs to stick with non-compound-pages
> > for the foreseeable future.
> >
> Hmm, I was sort off wondering that fsdax could move to compound pages too as
> opposed to base pages, albeit not necessarily using the vmemmap page reuse
> as it splits pages IIUC.

I'm not sure compound pages for fsdax would work long term because
there's no infrastructure to reassemble compound pages after a split.
So if you fracture a block and then coalesce it back to a 2MB or 1GB
aligned block there's nothing to go fixup the compound page... unless
the filesystem wants to get into mm metadata fixups.
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WARNING: multiple messages have this Message-ID (diff)
From: Dan Williams <dan.j.williams@intel.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Linux MM <linux-mm@kvack.org>, Ira Weiny <ira.weiny@intel.com>,
	 linux-nvdimm <linux-nvdimm@lists.01.org>,
	Matthew Wilcox <willy@infradead.org>,
	 Jason Gunthorpe <jgg@ziepe.ca>, Jane Chu <jane.chu@oracle.com>,
	 Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages
Date: Tue, 23 Feb 2021 10:18:30 -0800	[thread overview]
Message-ID: <CAPcyv4ixBjf7w-FtSaVOHoXccVag=gw7-mmaMYReV92pczy2tA@mail.gmail.com> (raw)
In-Reply-To: <e9e24d05-79e7-275a-530d-fc3b5041845d@oracle.com>

On Tue, Feb 23, 2021 at 9:19 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> On 2/23/21 4:50 PM, Dan Williams wrote:
> > On Tue, Feb 23, 2021 at 7:46 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >> On 2/22/21 8:37 PM, Dan Williams wrote:
> >>> On Mon, Feb 22, 2021 at 3:24 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >>>> On 2/20/21 1:43 AM, Dan Williams wrote:
> >>>>> On Tue, Dec 8, 2020 at 9:59 PM John Hubbard <jhubbard@nvidia.com> wrote:
> >>>>>> On 12/8/20 9:28 AM, Joao Martins wrote:
>
> [...]
>
> >>> Don't get me wrong the
> >>> capability is still needed for filesystem-dax, but the distinction is
> >>> that vmemmap_populate_compound_pages() need never worry about an
> >>> altmap.
> >>>
> >> IMO there's not much added complexity strictly speaking about altmap. We still use the
> >> same vmemmap_{pmd,pte,pgd}_populate helpers which just pass an altmap. So whatever it is
> >> being maintained for fsdax or other altmap consumers (e.g. we seem to be working towards
> >> hotplug making use of it) we are using it in the exact same way.
> >>
> >> The complexity of the future vmemmap_populate_compound_pages() has more to do with reusing
> >> vmemmap blocks allocated in previous vmemmap pages, and preserving that across section
> >> onlining (for 1G pages).
> >
> > True, I'm less worried about the complexity as much as
> > opportunistically converting configurations to RAM backed pages. It's
> > already the case that poison handling is page mapping size aligned for
> > device-dax, and filesystem-dax needs to stick with non-compound-pages
> > for the foreseeable future.
> >
> Hmm, I was sort off wondering that fsdax could move to compound pages too as
> opposed to base pages, albeit not necessarily using the vmemmap page reuse
> as it splits pages IIUC.

I'm not sure compound pages for fsdax would work long term because
there's no infrastructure to reassemble compound pages after a split.
So if you fracture a block and then coalesce it back to a 2MB or 1GB
aligned block there's nothing to go fixup the compound page... unless
the filesystem wants to get into mm metadata fixups.


  reply	other threads:[~2021-02-23 18:18 UTC|newest]

Thread overview: 147+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 17:28 [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps Joao Martins
2020-12-08 17:28 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  5:59   ` John Hubbard
2020-12-09  5:59     ` John Hubbard
2020-12-09  6:33     ` Matthew Wilcox
2020-12-09  6:33       ` Matthew Wilcox
2020-12-09 13:12       ` Joao Martins
2020-12-09 13:12         ` Joao Martins
2021-02-20  1:43     ` Dan Williams
2021-02-20  1:43       ` Dan Williams
2021-02-22 11:24       ` Joao Martins
2021-02-22 11:24         ` Joao Martins
2021-02-22 20:37         ` Dan Williams
2021-02-22 20:37           ` Dan Williams
2021-02-23 15:46           ` Joao Martins
2021-02-23 15:46             ` Joao Martins
2021-02-23 16:50             ` Dan Williams
2021-02-23 16:50               ` Dan Williams
2021-02-23 17:18               ` Joao Martins
2021-02-23 17:18                 ` Joao Martins
2021-02-23 18:18                 ` Dan Williams [this message]
2021-02-23 18:18                   ` Dan Williams
2021-03-10 18:12           ` Joao Martins
2021-03-10 18:12             ` Joao Martins
2021-03-12  5:54             ` Dan Williams
2021-03-12  5:54               ` Dan Williams
2021-02-20  1:24   ` Dan Williams
2021-02-20  1:24     ` Dan Williams
2021-02-22 11:09     ` Joao Martins
2021-02-22 11:09       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 2/9] sparse-vmemmap: Consolidate arguments in vmemmap section populate Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  6:16   ` John Hubbard
2020-12-09  6:16     ` John Hubbard
2020-12-09 13:51     ` Joao Martins
2020-12-09 13:51       ` Joao Martins
2021-02-20  1:49   ` Dan Williams
2021-02-20  1:49     ` Dan Williams
2021-02-22 11:26     ` Joao Martins
2021-02-22 11:26       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given mhp_params::align Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:38   ` Joao Martins
2020-12-08 17:38     ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  3:34   ` Dan Williams
2021-02-20  3:34     ` Dan Williams
2021-02-22 11:42     ` Joao Martins
2021-02-22 11:42       ` Joao Martins
2021-02-22 22:40       ` Dan Williams
2021-02-22 22:40         ` Dan Williams
2021-02-23 15:46         ` Joao Martins
2021-02-23 15:46           ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 4/9] mm/page_alloc: Reuse tail struct pages for compound pagemaps Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  6:17   ` Dan Williams
2021-02-20  6:17     ` Dan Williams
2021-02-22 12:01     ` Joao Martins
2021-02-22 12:01       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 5/9] device-dax: Compound pagemap support Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:49   ` Jason Gunthorpe
2020-12-09 11:05     ` Joao Martins
2020-12-09 11:05       ` Joao Martins
2020-12-09 15:15       ` Jason Gunthorpe
2020-12-09 16:02         ` Joao Martins
2020-12-09 16:02           ` Joao Martins
2020-12-09 16:24           ` Jason Gunthorpe
2020-12-09 17:27             ` Joao Martins
2020-12-09 17:27               ` Joao Martins
2020-12-09 18:14             ` Matthew Wilcox
2020-12-09 18:14               ` Matthew Wilcox
2020-12-09 19:08               ` Jason Gunthorpe
2020-12-10 15:43               ` Joao Martins
2020-12-10 15:43                 ` Joao Martins
2020-12-09  4:40   ` John Hubbard
2020-12-09  4:40     ` John Hubbard
2020-12-09 13:44     ` Joao Martins
2020-12-09 13:44       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 7/9] mm/gup: Decrement head page " Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:34   ` Jason Gunthorpe
2020-12-09  5:06     ` John Hubbard
2020-12-09  5:06       ` John Hubbard
2020-12-09 13:43       ` Jason Gunthorpe
2020-12-09 12:17     ` Joao Martins
2020-12-09 12:17       ` Joao Martins
2020-12-17 19:05     ` Joao Martins
2020-12-17 19:05       ` Joao Martins
2020-12-17 20:05       ` Jason Gunthorpe
2020-12-17 22:34         ` Joao Martins
2020-12-17 22:34           ` Joao Martins
2020-12-18 14:25           ` Jason Gunthorpe
2020-12-19  2:06         ` John Hubbard
2020-12-19  2:06           ` John Hubbard
2020-12-19 13:10           ` Joao Martins
2020-12-19 13:10             ` Joao Martins
2020-12-08 17:29 ` [PATCH RFC 8/9] RDMA/umem: batch page unpin in __ib_mem_release() Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:29   ` Jason Gunthorpe
2020-12-09 10:59     ` Joao Martins
2020-12-09 10:59       ` Joao Martins
2020-12-19 13:15       ` Joao Martins
2020-12-19 13:15         ` Joao Martins
2020-12-09  5:18   ` John Hubbard
2020-12-09  5:18     ` John Hubbard
2020-12-08 17:29 ` [PATCH RFC 9/9] mm: Add follow_devmap_page() for devdax vmas Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:57   ` Jason Gunthorpe
2020-12-09  8:05     ` Christoph Hellwig
2020-12-09  8:05       ` Christoph Hellwig
2020-12-09 11:19     ` Joao Martins
2020-12-09 11:19       ` Joao Martins
2020-12-09  5:23   ` John Hubbard
2020-12-09  5:23     ` John Hubbard
2020-12-09  9:38 ` [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps David Hildenbrand
2020-12-09  9:38   ` David Hildenbrand
2020-12-09  9:52 ` [External] " Muchun Song
2020-12-09  9:52   ` Muchun Song
2021-02-20  1:18 ` Dan Williams
2021-02-20  1:18   ` Dan Williams
2021-02-22 11:06   ` Joao Martins
2021-02-22 11:06     ` Joao Martins
2021-02-22 14:32     ` Joao Martins
2021-02-22 14:32       ` Joao Martins
2021-02-23 16:28   ` Joao Martins
2021-02-23 16:28     ` Joao Martins
2021-02-23 16:44     ` Dan Williams
2021-02-23 16:44       ` Dan Williams
2021-02-23 17:15       ` Joao Martins
2021-02-23 17:15         ` Joao Martins
2021-02-23 18:15         ` Dan Williams
2021-02-23 18:15           ` Dan Williams
2021-02-23 18:54       ` Jason Gunthorpe
2021-02-23 22:48         ` Dan Williams
2021-02-23 22:48           ` Dan Williams
2021-02-23 23:07           ` Jason Gunthorpe
2021-02-24  0:14             ` Dan Williams
2021-02-24  0:14               ` Dan Williams
2021-02-24  1:00               ` Jason Gunthorpe
2021-02-24  1:32                 ` Dan Williams
2021-02-24  1:32                   ` Dan Williams

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