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From: Jane Chu <jane.chu@oracle.com>
To: Joao Martins <joao.m.martins@oracle.com>,
	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>,
	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 04/14] mm/memremap: add ZONE_DEVICE support for compound pages
Date: Wed, 21 Jul 2021 17:38:11 -0700	[thread overview]
Message-ID: <edf0358d-7ef6-d18e-a45d-f36449b116f5@oracle.com> (raw)
In-Reply-To: <d73793a8-7540-c473-0e30-0880341c2baf@oracle.com>


On 7/15/2021 5:52 AM, Joao Martins wrote:
>>> +               __init_zone_device_page(page + i, pfn + i, zone_idx,
>>> +                                       nid, pgmap);
>>> +               prep_compound_tail(page, i);
>>> +
>>> +               /*
>>> +                * The first and second tail pages need to
>>> +                * initialized first, hence the head page is
>>> +                * prepared last.
>> I'd change this comment to say why rather than restate what can be
>> gleaned from the code. It's actually not clear to me why this order is
>> necessary.
>>
> So the first tail page stores mapcount_ptr and compound order, and the
> second tail page stores pincount_ptr. prep_compound_head() does this:
> 
> 	set_compound_order(page, order);
> 	atomic_set(compound_mapcount_ptr(page), -1);
> 	if (hpage_pincount_available(page))
> 		atomic_set(compound_pincount_ptr(page), 0);
> 
> So we need those tail pages initialized first prior to initializing the head.
> 
> I can expand the comment above to make it clear why we need first and second tail pages.
> 

Perhaps just say
   The reason prep_compound_head() is called after the 1st and 2nd tail
   pages have been initialized is: so it overwrites some of the tail page
   fields setup by __init_zone_device_page(), rather than the other way 
around.
?

thanks,
-jane

  parent reply	other threads:[~2021-07-22  0:38 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 [this message]
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
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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