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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>
Subject: Re: [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps
Date: Tue, 23 Feb 2021 08:44:52 -0800	[thread overview]
Message-ID: <CAPcyv4joomjhZYaCBNrYjvATSYgECfHYOZy=n_QVKqX7D_ReZQ@mail.gmail.com> (raw)
In-Reply-To: <6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com>

On Tue, Feb 23, 2021 at 8:30 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> On 2/20/21 1:18 AM, Dan Williams wrote:
> > On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >> Patch 6 - 8: Optimize grabbing/release a page refcount changes given that we
> >> are working with compound pages i.e. we do 1 increment/decrement to the head
> >> page for a given set of N subpages compared as opposed to N individual writes.
> >> {get,pin}_user_pages_fast() for zone_device with compound pagemap consequently
> >> improves considerably, and unpin_user_pages() improves as well when passed a
> >> set of consecutive pages:
> >>
> >>                                            before          after
> >>     (get_user_pages_fast 1G;2M page size) ~75k  us -> ~3.2k ; ~5.2k us
> >>     (pin_user_pages_fast 1G;2M page size) ~125k us -> ~3.4k ; ~5.5k us
> >
> > Compelling!
> >
>
> BTW is there any reason why we don't support pin_user_pages_fast() with FOLL_LONGTERM for
> device-dax?
>

Good catch.

Must have been an oversight of the conversion. FOLL_LONGTERM collides
with filesystem operations, but not device-dax. In fact that's the
motivation for device-dax in the first instance, no need to coordinate
runtime physical address layout changes because the device is
statically allocated.

> Looking at the history, I understand that fsdax can't support it atm, but I am not sure
> that the same holds for device-dax. I have this small chunk (see below the scissors mark)
> which relaxes this for a pgmap of type MEMORY_DEVICE_GENERIC, albeit not sure if there is
> a fundamental issue for the other types that makes this an unwelcoming change.
>
>         Joao
>
> --------------------->8---------------------
>
> Subject: [PATCH] mm/gup: allow FOLL_LONGTERM pin-fast for
>  MEMORY_DEVICE_GENERIC
>
> The downside would be one extra lookup in dev_pagemap tree
> for other pgmap->types (P2P, FSDAX, PRIVATE). But just one
> per gup-fast() call.

I'd guess a dev_pagemap lookup is faster than a get_user_pages slow
path. It should be measurable that this change is at least as fast or
faster than falling back to the slow path, but it would be good to
measure.

Code changes look good to me.

>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  include/linux/mm.h |  5 +++++
>  mm/gup.c           | 24 +++++++++++++-----------
>  2 files changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 32f0c3986d4f..c89a049bbd7a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1171,6 +1171,11 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
>                 page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
>  }
>
> +static inline bool devmap_longterm_available(const struct dev_pagemap *pgmap)
> +{

I'd call this devmap_can_longterm().

> +       return pgmap->type == MEMORY_DEVICE_GENERIC;
> +}
> +
>  /* 127: arbitrary random number, small enough to assemble well */
>  #define page_ref_zero_or_close_to_overflow(page) \
>         ((unsigned int) page_ref_count(page) + 127u <= 127u)
> diff --git a/mm/gup.c b/mm/gup.c
> index 222d1fdc5cfa..03e370d360e6 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2092,14 +2092,18 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned
> long end,
>                         goto pte_unmap;
>
>                 if (pte_devmap(pte)) {
> -                       if (unlikely(flags & FOLL_LONGTERM))
> -                               goto pte_unmap;
> -
>                         pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
>                         if (unlikely(!pgmap)) {
>                                 undo_dev_pagemap(nr, nr_start, flags, pages);
>                                 goto pte_unmap;
>                         }
> +
> +                       if (unlikely(flags & FOLL_LONGTERM) &&
> +                           !devmap_longterm_available(pgmap)) {
> +                               undo_dev_pagemap(nr, nr_start, flags, pages);
> +                               goto pte_unmap;
> +                       }
> +
>                 } else if (pte_special(pte))
>                         goto pte_unmap;
>
> @@ -2195,6 +2199,10 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>                         return 0;
>                 }
>
> +               if (unlikely(flags & FOLL_LONGTERM) &&
> +                   !devmap_longterm_available(pgmap))
> +                       return 0;
> +
> @@ -2356,12 +2364,9 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>         if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
>                 return 0;
>
> -       if (pmd_devmap(orig)) {
> -               if (unlikely(flags & FOLL_LONGTERM))
> -                       return 0;
> +       if (pmd_devmap(orig))
>                 return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
>                                              pages, nr);
> -       }
>
>         page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
>         refs = record_subpages(page, addr, end, pages + *nr);
> @@ -2390,12 +2395,9 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
>         if (!pud_access_permitted(orig, flags & FOLL_WRITE))
>                 return 0;
>
> -       if (pud_devmap(orig)) {
> -               if (unlikely(flags & FOLL_LONGTERM))
> -                       return 0;
> +       if (pud_devmap(orig))
>                 return __gup_device_huge_pud(orig, pudp, addr, end, flags,
>                                              pages, nr);
> -       }
>
>         page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
>         refs = record_subpages(page, addr, end, pages + *nr);
> --
> 2.17.1
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WARNING: multiple messages have this Message-ID
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>
Subject: Re: [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps
Date: Tue, 23 Feb 2021 08:44:52 -0800	[thread overview]
Message-ID: <CAPcyv4joomjhZYaCBNrYjvATSYgECfHYOZy=n_QVKqX7D_ReZQ@mail.gmail.com> (raw)
In-Reply-To: <6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com>

On Tue, Feb 23, 2021 at 8:30 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> On 2/20/21 1:18 AM, Dan Williams wrote:
> > On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
> >> Patch 6 - 8: Optimize grabbing/release a page refcount changes given that we
> >> are working with compound pages i.e. we do 1 increment/decrement to the head
> >> page for a given set of N subpages compared as opposed to N individual writes.
> >> {get,pin}_user_pages_fast() for zone_device with compound pagemap consequently
> >> improves considerably, and unpin_user_pages() improves as well when passed a
> >> set of consecutive pages:
> >>
> >>                                            before          after
> >>     (get_user_pages_fast 1G;2M page size) ~75k  us -> ~3.2k ; ~5.2k us
> >>     (pin_user_pages_fast 1G;2M page size) ~125k us -> ~3.4k ; ~5.5k us
> >
> > Compelling!
> >
>
> BTW is there any reason why we don't support pin_user_pages_fast() with FOLL_LONGTERM for
> device-dax?
>

Good catch.

Must have been an oversight of the conversion. FOLL_LONGTERM collides
with filesystem operations, but not device-dax. In fact that's the
motivation for device-dax in the first instance, no need to coordinate
runtime physical address layout changes because the device is
statically allocated.

> Looking at the history, I understand that fsdax can't support it atm, but I am not sure
> that the same holds for device-dax. I have this small chunk (see below the scissors mark)
> which relaxes this for a pgmap of type MEMORY_DEVICE_GENERIC, albeit not sure if there is
> a fundamental issue for the other types that makes this an unwelcoming change.
>
>         Joao
>
> --------------------->8---------------------
>
> Subject: [PATCH] mm/gup: allow FOLL_LONGTERM pin-fast for
>  MEMORY_DEVICE_GENERIC
>
> The downside would be one extra lookup in dev_pagemap tree
> for other pgmap->types (P2P, FSDAX, PRIVATE). But just one
> per gup-fast() call.

I'd guess a dev_pagemap lookup is faster than a get_user_pages slow
path. It should be measurable that this change is at least as fast or
faster than falling back to the slow path, but it would be good to
measure.

Code changes look good to me.

>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  include/linux/mm.h |  5 +++++
>  mm/gup.c           | 24 +++++++++++++-----------
>  2 files changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 32f0c3986d4f..c89a049bbd7a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1171,6 +1171,11 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
>                 page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
>  }
>
> +static inline bool devmap_longterm_available(const struct dev_pagemap *pgmap)
> +{

I'd call this devmap_can_longterm().

> +       return pgmap->type == MEMORY_DEVICE_GENERIC;
> +}
> +
>  /* 127: arbitrary random number, small enough to assemble well */
>  #define page_ref_zero_or_close_to_overflow(page) \
>         ((unsigned int) page_ref_count(page) + 127u <= 127u)
> diff --git a/mm/gup.c b/mm/gup.c
> index 222d1fdc5cfa..03e370d360e6 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2092,14 +2092,18 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned
> long end,
>                         goto pte_unmap;
>
>                 if (pte_devmap(pte)) {
> -                       if (unlikely(flags & FOLL_LONGTERM))
> -                               goto pte_unmap;
> -
>                         pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
>                         if (unlikely(!pgmap)) {
>                                 undo_dev_pagemap(nr, nr_start, flags, pages);
>                                 goto pte_unmap;
>                         }
> +
> +                       if (unlikely(flags & FOLL_LONGTERM) &&
> +                           !devmap_longterm_available(pgmap)) {
> +                               undo_dev_pagemap(nr, nr_start, flags, pages);
> +                               goto pte_unmap;
> +                       }
> +
>                 } else if (pte_special(pte))
>                         goto pte_unmap;
>
> @@ -2195,6 +2199,10 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>                         return 0;
>                 }
>
> +               if (unlikely(flags & FOLL_LONGTERM) &&
> +                   !devmap_longterm_available(pgmap))
> +                       return 0;
> +
> @@ -2356,12 +2364,9 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>         if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
>                 return 0;
>
> -       if (pmd_devmap(orig)) {
> -               if (unlikely(flags & FOLL_LONGTERM))
> -                       return 0;
> +       if (pmd_devmap(orig))
>                 return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
>                                              pages, nr);
> -       }
>
>         page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
>         refs = record_subpages(page, addr, end, pages + *nr);
> @@ -2390,12 +2395,9 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
>         if (!pud_access_permitted(orig, flags & FOLL_WRITE))
>                 return 0;
>
> -       if (pud_devmap(orig)) {
> -               if (unlikely(flags & FOLL_LONGTERM))
> -                       return 0;
> +       if (pud_devmap(orig))
>                 return __gup_device_huge_pud(orig, pudp, addr, end, flags,
>                                              pages, nr);
> -       }
>
>         page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
>         refs = record_subpages(page, addr, end, pages + *nr);
> --
> 2.17.1


  reply	other threads:[~2021-02-23 16:45 UTC|newest]

Thread overview: 147+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 17:28 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
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 [this message]
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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