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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>,
	Vishal Verma <vishal.l.verma@intel.com>,
	 Dave Jiang <dave.jiang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	 Matthew Wilcox <willy@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>,
	 Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	 Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Jonathan Corbet <corbet@lwn.net>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	 Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3 09/14] mm/page_alloc: reuse tail struct pages for compound pagemaps
Date: Wed, 28 Jul 2021 00:28:25 -0700	[thread overview]
Message-ID: <CAPcyv4gDndA612+1BKZcR518K_Rt3Q1gWpqK24KOqvoFp_PNGg@mail.gmail.com> (raw)
In-Reply-To: <20210714193542.21857-10-joao.m.martins@oracle.com>

On Wed, Jul 14, 2021 at 12:36 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> Currently memmap_init_zone_device() ends up initializing 32768 pages
> when it only needs to initialize 128 given tail page reuse. That
> number is worse with 1GB compound page geometries, 262144 instead of
> 128. Update memmap_init_zone_device() to skip redundant
> initialization, detailed below.
>
> When a pgmap @geometry is set, all pages are mapped at a given huge page
> alignment and use compound pages to describe them as opposed to a
> struct per 4K.
>
> With @geometry > PAGE_SIZE and when struct pages are stored in ram
> (!altmap) most tail pages are reused. Consequently, the amount of unique
> struct pages is a lot smaller that the total amount of struct pages
> being mapped.
>
> The altmap path is left alone since it does not support memory savings
> based on compound pagemap geometries.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  mm/page_alloc.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 188cb5f8c308..96975edac0a8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6600,11 +6600,23 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
>  static void __ref memmap_init_compound(struct page *page, unsigned long pfn,
>                                         unsigned long zone_idx, int nid,
>                                         struct dev_pagemap *pgmap,
> +                                       struct vmem_altmap *altmap,
>                                         unsigned long nr_pages)
>  {
>         unsigned int order_align = order_base_2(nr_pages);
>         unsigned long i;
>
> +       /*
> +        * With compound page geometry and when struct pages are stored in ram
> +        * (!altmap) most tail pages are reused. Consequently, the amount of
> +        * unique struct pages to initialize is a lot smaller that the total
> +        * amount of struct pages being mapped.
> +        * See vmemmap_populate_compound_pages().
> +        */
> +       if (!altmap)
> +               nr_pages = min_t(unsigned long, nr_pages,

What's the scenario where nr_pages is < 128? Shouldn't alignment
already be guaranteed?

> +                                2 * (PAGE_SIZE/sizeof(struct page)));


> +
>         __SetPageHead(page);
>
>         for (i = 1; i < nr_pages; i++) {
> @@ -6657,7 +6669,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
>                         continue;
>
>                 memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
> -                                    pfns_per_compound);
> +                                    altmap, pfns_per_compound);

This feels odd, memmap_init_compound() doesn't really care about
altmap, what do you think about explicitly calculating the parameters
that memmap_init_compound() needs and passing them in?

Not a strong requirement to change, but take another look at let me know.



>         }
>
>         pr_info("%s initialised %lu pages in %ums\n", __func__,
> --
> 2.17.1
>

  reply	other threads:[~2021-07-28  7:28 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14 19:35 [PATCH v3 00/14] mm, sparse-vmemmap: Introduce " Joao Martins
2021-07-14 19:35 ` [PATCH v3 01/14] memory-failure: fetch compound_head after pgmap_pfn_valid() Joao Martins
2021-07-15  0:17   ` Dan Williams
2021-07-15  2:51   ` [External] " Muchun Song
2021-07-15  6:40     ` Christoph Hellwig
2021-07-15  9:19       ` Muchun Song
2021-07-15 13:17     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 02/14] mm/page_alloc: split prep_compound_page into head and tail subparts Joao Martins
2021-07-15  0:19   ` Dan Williams
2021-07-15  2:53   ` [External] " Muchun Song
2021-07-15 13:17     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 03/14] mm/page_alloc: refactor memmap_init_zone_device() page init Joao Martins
2021-07-15  0:20   ` Dan Williams
2021-07-14 19:35 ` [PATCH v3 04/14] mm/memremap: add ZONE_DEVICE support for compound pages Joao Martins
2021-07-15  1:08   ` Dan Williams
2021-07-15 12:52     ` Joao Martins
2021-07-15 13:06       ` Joao Martins
2021-07-15 19:48       ` Dan Williams
2021-07-30 16:13         ` Joao Martins
2021-07-22  0:38       ` Jane Chu
2021-07-22 10:56         ` Joao Martins
2021-07-15 12:59     ` Christoph Hellwig
2021-07-15 13:15       ` Joao Martins
2021-07-15  6:48   ` Christoph Hellwig
2021-07-15 13:15     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 05/14] mm/sparse-vmemmap: add a pgmap argument to section activation Joao Martins
2021-07-28  5:56   ` Dan Williams
2021-07-28  9:43     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 06/14] mm/sparse-vmemmap: refactor core of vmemmap_populate_basepages() to helper Joao Martins
2021-07-28  6:04   ` Dan Williams
2021-07-28 10:48     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 07/14] mm/hugetlb_vmemmap: move comment block to Documentation/vm Joao Martins
2021-07-15  2:47   ` [External] " Muchun Song
2021-07-15 13:16     ` Joao Martins
2021-07-28  6:09   ` Dan Williams
2021-07-14 19:35 ` [PATCH v3 08/14] mm/sparse-vmemmap: populate compound pagemaps Joao Martins
2021-07-28  6:55   ` Dan Williams
2021-07-28 15:35     ` Joao Martins
2021-07-28 18:03       ` Dan Williams
2021-07-28 18:54         ` Joao Martins
2021-07-28 20:04           ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 09/14] mm/page_alloc: reuse tail struct pages for " Joao Martins
2021-07-28  7:28   ` Dan Williams [this message]
2021-07-28 15:56     ` Joao Martins
2021-07-28 16:08       ` Dan Williams
2021-07-28 16:12         ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 10/14] device-dax: use ALIGN() for determining pgoff Joao Martins
2021-07-28  7:29   ` Dan Williams
2021-07-28 15:56     ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 11/14] device-dax: ensure dev_dax->pgmap is valid for dynamic devices Joao Martins
2021-07-28  7:30   ` Dan Williams
2021-07-28 15:56     ` Joao Martins
2021-08-06 12:28       ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 12/14] device-dax: compound pagemap support Joao Martins
2021-07-14 23:36   ` Dan Williams
2021-07-15 12:00     ` Joao Martins
2021-07-27 23:51       ` Dan Williams
2021-07-28  9:36         ` Joao Martins
2021-07-28 18:51           ` Dan Williams
2021-07-28 18:59             ` Joao Martins
2021-07-28 19:03               ` Dan Williams
2021-07-14 19:35 ` [PATCH v3 13/14] mm/gup: grab head page refcount once for group of subpages Joao Martins
2021-07-28 19:55   ` Dan Williams
2021-07-28 20:07     ` Joao Martins
2021-07-28 20:23       ` Dan Williams
2021-08-25 19:10         ` Joao Martins
2021-08-25 19:15           ` Matthew Wilcox
2021-08-25 19:26             ` Joao Martins
2021-07-14 19:35 ` [PATCH v3 14/14] mm/sparse-vmemmap: improve memory savings for compound pud geometry Joao Martins
2021-07-28 20:03   ` Dan Williams
2021-07-28 20:08     ` Joao Martins
2021-07-14 21:48 ` [PATCH v3 00/14] mm, sparse-vmemmap: Introduce compound pagemaps Andrew Morton
2021-07-14 23:47   ` Dan Williams
2021-07-22  2:24   ` Matthew Wilcox
2021-07-22 10:53     ` Joao Martins
2021-07-27 23:23       ` Dan Williams
2021-08-02 10:40         ` Joao Martins
2021-08-02 14:06           ` Dan Williams

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