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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 4/9] mm/page_alloc: Reuse tail struct pages for compound pagemaps
Date: Fri, 19 Feb 2021 22:17:24 -0800	[thread overview]
Message-ID: <CAPcyv4hw574wYUa0qzz+pQrB4K11R618Moh30mvLz8GLNDw=5w@mail.gmail.com> (raw)
In-Reply-To: <20201208172901.17384-6-joao.m.martins@oracle.com>

On Tue, Dec 8, 2020 at 9:31 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> When PGMAP_COMPOUND is set, all pages are onlined at a given huge page
> alignment and using compound pages to describe them as opposed to a
> struct per 4K.
>

Same s/online/mapped/ comment as other changelogs.

> To minimize struct page overhead and given the usage of compound pages we
> utilize the fact that most tail pages look the same, we online the
> subsection while pointing to the same pages. Thus request VMEMMAP_REUSE
> in add_pages.
>
> With VMEMMAP_REUSE, provided we reuse most tail pages the amount of
> struct pages we need to initialize is a lot smaller that the total
> amount of structs we would normnally online. Thus allow an @init_order
> to be passed to specify how much pages we want to prep upon creating a
> compound page.
>
> Finally when onlining all struct pages in memmap_init_zone_device, make
> sure that we only initialize the unique struct pages i.e. the first 2
> 4K pages from @align which means 128 struct pages out of 32768 for 2M
> @align or 262144 for a 1G @align.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  mm/memremap.c   |  4 +++-
>  mm/page_alloc.c | 23 ++++++++++++++++++++---
>  2 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index ecfa74848ac6..3eca07916b9d 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -253,8 +253,10 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
>                         goto err_kasan;
>                 }
>
> -               if (pgmap->flags & PGMAP_COMPOUND)
> +               if (pgmap->flags & PGMAP_COMPOUND) {
>                         params->align = pgmap->align;
> +                       params->flags = MEMHP_REUSE_VMEMMAP;

The "reuse" naming is not my favorite. Yes, page reuse is happening,
but what is more relevant is that the vmemmap is in a given minimum
page size mode. So it's less of a flag and more of enum that selects
between PAGE_SIZE, HPAGE_SIZE, and PUD_PAGE_SIZE (GPAGE_SIZE?).

> +               }
>
>                 error = arch_add_memory(nid, range->start, range_len(range),
>                                         params);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9716ecd58e29..180a7d4e9285 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -691,10 +691,11 @@ void free_compound_page(struct page *page)
>         __free_pages_ok(page, compound_order(page), FPI_NONE);
>  }
>
> -void prep_compound_page(struct page *page, unsigned int order)
> +static void __prep_compound_page(struct page *page, unsigned int order,
> +                                unsigned int init_order)
>  {
>         int i;
> -       int nr_pages = 1 << order;
> +       int nr_pages = 1 << init_order;
>
>         __SetPageHead(page);
>         for (i = 1; i < nr_pages; i++) {
> @@ -711,6 +712,11 @@ void prep_compound_page(struct page *page, unsigned int order)
>                 atomic_set(compound_pincount_ptr(page), 0);
>  }
>
> +void prep_compound_page(struct page *page, unsigned int order)
> +{
> +       __prep_compound_page(page, order, order);
> +}
> +
>  #ifdef CONFIG_DEBUG_PAGEALLOC
>  unsigned int _debug_guardpage_minorder;
>
> @@ -6108,6 +6114,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>  }
>
>  #ifdef CONFIG_ZONE_DEVICE
> +
> +#define MEMMAP_COMPOUND_SIZE (2 * (PAGE_SIZE/sizeof(struct page)))
> +
>  void __ref memmap_init_zone_device(struct zone *zone,
>                                    unsigned long start_pfn,
>                                    unsigned long nr_pages,
> @@ -6138,6 +6147,12 @@ void __ref memmap_init_zone_device(struct zone *zone,
>         for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>                 struct page *page = pfn_to_page(pfn);
>
> +               /* Skip already initialized pages. */
> +               if (compound && (pfn % align >= MEMMAP_COMPOUND_SIZE)) {
> +                       pfn = ALIGN(pfn, align) - 1;
> +                       continue;
> +               }
> +
>                 __init_single_page(page, pfn, zone_idx, nid);
>
>                 /*
> @@ -6175,7 +6190,9 @@ void __ref memmap_init_zone_device(struct zone *zone,
>
>         if (compound) {
>                 for (pfn = start_pfn; pfn < end_pfn; pfn += align)
> -                       prep_compound_page(pfn_to_page(pfn), order_base_2(align));
> +                       __prep_compound_page(pfn_to_page(pfn),
> +                                          order_base_2(align),
> +                                          order_base_2(MEMMAP_COMPOUND_SIZE));
>         }

Alex did quite a bit of work to optimize this path, and this
organization appears to undo it. I'd prefer to keep it all in one loop
so a 'struct page' is only initialized once. Otherwise by the time the
above loop finishes and this one starts the 'struct page's are
probably cache cold again.

So I'd break prep_compoud_page into separate head and tail  init and
call them at the right time in one loop.
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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 4/9] mm/page_alloc: Reuse tail struct pages for compound pagemaps
Date: Fri, 19 Feb 2021 22:17:24 -0800	[thread overview]
Message-ID: <CAPcyv4hw574wYUa0qzz+pQrB4K11R618Moh30mvLz8GLNDw=5w@mail.gmail.com> (raw)
In-Reply-To: <20201208172901.17384-6-joao.m.martins@oracle.com>

On Tue, Dec 8, 2020 at 9:31 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> When PGMAP_COMPOUND is set, all pages are onlined at a given huge page
> alignment and using compound pages to describe them as opposed to a
> struct per 4K.
>

Same s/online/mapped/ comment as other changelogs.

> To minimize struct page overhead and given the usage of compound pages we
> utilize the fact that most tail pages look the same, we online the
> subsection while pointing to the same pages. Thus request VMEMMAP_REUSE
> in add_pages.
>
> With VMEMMAP_REUSE, provided we reuse most tail pages the amount of
> struct pages we need to initialize is a lot smaller that the total
> amount of structs we would normnally online. Thus allow an @init_order
> to be passed to specify how much pages we want to prep upon creating a
> compound page.
>
> Finally when onlining all struct pages in memmap_init_zone_device, make
> sure that we only initialize the unique struct pages i.e. the first 2
> 4K pages from @align which means 128 struct pages out of 32768 for 2M
> @align or 262144 for a 1G @align.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  mm/memremap.c   |  4 +++-
>  mm/page_alloc.c | 23 ++++++++++++++++++++---
>  2 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index ecfa74848ac6..3eca07916b9d 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -253,8 +253,10 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
>                         goto err_kasan;
>                 }
>
> -               if (pgmap->flags & PGMAP_COMPOUND)
> +               if (pgmap->flags & PGMAP_COMPOUND) {
>                         params->align = pgmap->align;
> +                       params->flags = MEMHP_REUSE_VMEMMAP;

The "reuse" naming is not my favorite. Yes, page reuse is happening,
but what is more relevant is that the vmemmap is in a given minimum
page size mode. So it's less of a flag and more of enum that selects
between PAGE_SIZE, HPAGE_SIZE, and PUD_PAGE_SIZE (GPAGE_SIZE?).

> +               }
>
>                 error = arch_add_memory(nid, range->start, range_len(range),
>                                         params);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9716ecd58e29..180a7d4e9285 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -691,10 +691,11 @@ void free_compound_page(struct page *page)
>         __free_pages_ok(page, compound_order(page), FPI_NONE);
>  }
>
> -void prep_compound_page(struct page *page, unsigned int order)
> +static void __prep_compound_page(struct page *page, unsigned int order,
> +                                unsigned int init_order)
>  {
>         int i;
> -       int nr_pages = 1 << order;
> +       int nr_pages = 1 << init_order;
>
>         __SetPageHead(page);
>         for (i = 1; i < nr_pages; i++) {
> @@ -711,6 +712,11 @@ void prep_compound_page(struct page *page, unsigned int order)
>                 atomic_set(compound_pincount_ptr(page), 0);
>  }
>
> +void prep_compound_page(struct page *page, unsigned int order)
> +{
> +       __prep_compound_page(page, order, order);
> +}
> +
>  #ifdef CONFIG_DEBUG_PAGEALLOC
>  unsigned int _debug_guardpage_minorder;
>
> @@ -6108,6 +6114,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>  }
>
>  #ifdef CONFIG_ZONE_DEVICE
> +
> +#define MEMMAP_COMPOUND_SIZE (2 * (PAGE_SIZE/sizeof(struct page)))
> +
>  void __ref memmap_init_zone_device(struct zone *zone,
>                                    unsigned long start_pfn,
>                                    unsigned long nr_pages,
> @@ -6138,6 +6147,12 @@ void __ref memmap_init_zone_device(struct zone *zone,
>         for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>                 struct page *page = pfn_to_page(pfn);
>
> +               /* Skip already initialized pages. */
> +               if (compound && (pfn % align >= MEMMAP_COMPOUND_SIZE)) {
> +                       pfn = ALIGN(pfn, align) - 1;
> +                       continue;
> +               }
> +
>                 __init_single_page(page, pfn, zone_idx, nid);
>
>                 /*
> @@ -6175,7 +6190,9 @@ void __ref memmap_init_zone_device(struct zone *zone,
>
>         if (compound) {
>                 for (pfn = start_pfn; pfn < end_pfn; pfn += align)
> -                       prep_compound_page(pfn_to_page(pfn), order_base_2(align));
> +                       __prep_compound_page(pfn_to_page(pfn),
> +                                          order_base_2(align),
> +                                          order_base_2(MEMMAP_COMPOUND_SIZE));
>         }

Alex did quite a bit of work to optimize this path, and this
organization appears to undo it. I'd prefer to keep it all in one loop
so a 'struct page' is only initialized once. Otherwise by the time the
above loop finishes and this one starts the 'struct page's are
probably cache cold again.

So I'd break prep_compoud_page into separate head and tail  init and
call them at the right time in one loop.


  reply	other threads:[~2021-02-20  6:17 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 " 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 [this message]
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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