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From: Joao Martins <joao.m.martins@oracle.com>
To: Dan Williams <dan.j.williams@intel.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 17:12:46 +0100	[thread overview]
Message-ID: <6969bf47-2405-a3bc-59c6-5dd665bfb70e@oracle.com> (raw)
In-Reply-To: <CAPcyv4iROoeKcVTKpVyUr+hrmKJxj7QnCS5pGPAnhLDvChHXJw@mail.gmail.com>



On 7/28/21 5:08 PM, Dan Williams wrote:
> On Wed, Jul 28, 2021 at 8:56 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> On 7/28/21 8:28 AM, Dan Williams wrote:
>>> On Wed, Jul 14, 2021 at 12:36 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>>>>
>>>> +       /*
>>>> +        * 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?
>>>
>> Oh yeah, that's right.
>>
>>>> +                                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.
>>>
>>
>> Yeah, memmap_init_compound() indeed doesn't care about @altmap itself -- but a previous
>> comment was to abstract this away in memmap_init_compound() given the mix of complexity in
>> memmap_init_zone_device() PAGE_SIZE geometry case and the compound case:
>>
>> https://lore.kernel.org/linux-mm/CAPcyv4gtSqfmuAaX9cs63OvLkf-h4B_5fPiEnM9p9cqLZztXpg@mail.gmail.com/
>>
>> Before this was called @ntails above and I hide that calculation in memmap_init_compound().
>>
>> But I can move this back to the caller:
>>
>> memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
>>         (!altmap ? 2 * (PAGE_SIZE/sizeof(struct page))) : pfns_per_compound);
>>
>> Or with another helper like:
>>
>> #define compound_nr_pages(__altmap, __nr_pages) \
>>                 (!__altmap ? 2 * (PAGE_SIZE/sizeof(struct page))) : __nr_pages);
>>
>> memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
>>                      compound_nr_pages(altmap, pfns_per_compound));
> 
> I like the helper, but I'd go further to make it a function with a
> comment that it is a paired / mild layering violation with explicit
> knowledge of how the sparse_vmemmap() internals handle compound pages
> in the presence of an altmap. I.e. if someone later goes to add altmap
> support, leave them a breadcrumb that they need to update both
> locations.
> 
OK, got it.

  reply	other threads:[~2021-07-28 16:13 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
2021-07-28 15:56     ` Joao Martins
2021-07-28 16:08       ` Dan Williams
2021-07-28 16:12         ` Joao Martins [this message]
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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