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.
next prev parent 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 compound pagemaps 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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