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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>,
	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 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size
Date: Mon, 22 Feb 2021 11:42:28 +0000	[thread overview]
Message-ID: <621ff98b-cb75-e4d7-8f09-882cb2b984d2@oracle.com> (raw)
In-Reply-To: <CAPcyv4ixD6_KEpuXkpeH6JNLvoahch8rm8J55o1B97ghrtcbjQ@mail.gmail.com>



On 2/20/21 3:34 AM, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> Introduce a new flag, MEMHP_REUSE_VMEMMAP, which signals that
>> struct pages are onlined with a given alignment, and should reuse the
>> tail pages vmemmap areas. On that circunstamce we reuse the PFN backing
> 
> s/On that circunstamce we reuse/Reuse/
> 
> Kills a "we" and switches to imperative tense. I noticed a couple
> other "we"s in the previous patches, but this crossed my threshold to
> make a comment.
> 
/me nods. Will fix.

>> only the tail pages subsections, while letting the head page PFN remain
>> different. This presumes that the backing page structs are compound
>> pages, such as the case for compound pagemaps (i.e. ZONE_DEVICE with
>> PGMAP_COMPOUND set)
>>
>> On 2M compound pagemaps, it lets us save 6 pages out of the 8 necessary
> 
> s/lets us save/saves/
> 
Will fix.

>> PFNs necessary
> 
> s/8 necessary PFNs necessary/8 PFNs necessary/

Will fix.

> 
>> to describe the subsection's 32K struct pages we are
>> onlining.
> 
> s/we are onlining/being mapped/
> 
> ...because ZONE_DEVICE pages are never "onlined".
> 
>> On a 1G compound pagemap it let us save 4096 pages.
> 
> s/lets us save/saves/
> 

Will fix both.

>>
>> Sections are 128M (or bigger/smaller),
> 
> Huh?
> 

Section size is arch-dependent if we are being hollistic.
On x86 it's 64M, 128M or 512M right?

 #ifdef CONFIG_X86_32
 # ifdef CONFIG_X86_PAE
 #  define SECTION_SIZE_BITS     29
 #  define MAX_PHYSMEM_BITS      36
 # else
 #  define SECTION_SIZE_BITS     26
 #  define MAX_PHYSMEM_BITS      32
 # endif
 #else /* CONFIG_X86_32 */
 # define SECTION_SIZE_BITS      27 /* matt - 128 is convenient right now */
 # define MAX_PHYSMEM_BITS       (pgtable_l5_enabled() ? 52 : 46)
 #endif

Also, me pointing about section sizes, is because a 1GB+ page vmemmap population will
cross sections in how sparsemem populates the vmemmap. And on that case we gotta reuse the
the PTE/PMD pages across multiple invocations of vmemmap_populate_basepages(). Either
that, or looking at the previous page PTE, but that might be ineficient.

>> @@ -229,38 +235,95 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
>>         for (; addr < end; addr += PAGE_SIZE) {
>>                 pgd = vmemmap_pgd_populate(addr, node);
>>                 if (!pgd)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 p4d = vmemmap_p4d_populate(pgd, addr, node);
>>                 if (!p4d)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 pud = vmemmap_pud_populate(p4d, addr, node);
>>                 if (!pud)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 pmd = vmemmap_pmd_populate(pud, addr, node);
>>                 if (!pmd)
>> -                       return -ENOMEM;
>> -               pte = vmemmap_pte_populate(pmd, addr, node, altmap);
>> +                       return NULL;
>> +               pte = vmemmap_pte_populate(pmd, addr, node, altmap, block);
>>                 if (!pte)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
>>         }
>>
>> +       return __va(__pfn_to_phys(pte_pfn(*pte)));
>> +}
>> +
>> +int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
>> +                                        int node, struct vmem_altmap *altmap)
>> +{
>> +       if (!__vmemmap_populate_basepages(start, end, node, altmap, NULL))
>> +               return -ENOMEM;
>>         return 0;
>>  }
>>
>> +static struct page * __meminit vmemmap_populate_reuse(unsigned long start,
>> +                                       unsigned long end, int node,
>> +                                       struct vmem_context *ctx)
>> +{
>> +       unsigned long size, addr = start;
>> +       unsigned long psize = PHYS_PFN(ctx->align) * sizeof(struct page);
>> +
>> +       size = min(psize, end - start);
>> +
>> +       for (; addr < end; addr += size) {
>> +               unsigned long head = addr + PAGE_SIZE;
>> +               unsigned long tail = addr;
>> +               unsigned long last = addr + size;
>> +               void *area;
>> +
>> +               if (ctx->block_page &&
>> +                   IS_ALIGNED((addr - ctx->block_page), psize))
>> +                       ctx->block = NULL;
>> +
>> +               area  = ctx->block;
>> +               if (!area) {
>> +                       if (!__vmemmap_populate_basepages(addr, head, node,
>> +                                                         ctx->altmap, NULL))
>> +                               return NULL;
>> +
>> +                       tail = head + PAGE_SIZE;
>> +                       area = __vmemmap_populate_basepages(head, tail, node,
>> +                                                           ctx->altmap, NULL);
>> +                       if (!area)
>> +                               return NULL;
>> +
>> +                       ctx->block = area;
>> +                       ctx->block_page = addr;
>> +               }
>> +
>> +               if (!__vmemmap_populate_basepages(tail, last, node,
>> +                                                 ctx->altmap, area))
>> +                       return NULL;
>> +       }
> 
> I think that compound page accounting and combined altmap accounting
> makes this difficult to read, and I think the compound page case
> deserves it's own first class loop rather than reusing
> vmemmap_populate_basepages(). With the suggestion to drop altmap
> support I'd expect a vmmemap_populate_compound that takes a compound
> page size and goes the right think with respect to mapping all the
> tail pages to the same pfn.
> 
I can move this to a separate loop as suggested.

But to be able to map all tail pages in one call of vmemmap_populate_compound()
this might requires changes in sparsemem generic code that I am not so sure
they are warranted the added complexity. Otherwise I'll have to probably keep
this logic of @ctx to be able to pass the page to be reused (i.e. @block and
@block_page). That's actually the main reason that made me introduce
a struct vmem_context.
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WARNING: multiple messages have this Message-ID
From: Joao Martins <joao.m.martins@oracle.com>
To: Dan Williams <dan.j.williams@intel.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 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size
Date: Mon, 22 Feb 2021 11:42:28 +0000	[thread overview]
Message-ID: <621ff98b-cb75-e4d7-8f09-882cb2b984d2@oracle.com> (raw)
In-Reply-To: <CAPcyv4ixD6_KEpuXkpeH6JNLvoahch8rm8J55o1B97ghrtcbjQ@mail.gmail.com>



On 2/20/21 3:34 AM, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> Introduce a new flag, MEMHP_REUSE_VMEMMAP, which signals that
>> struct pages are onlined with a given alignment, and should reuse the
>> tail pages vmemmap areas. On that circunstamce we reuse the PFN backing
> 
> s/On that circunstamce we reuse/Reuse/
> 
> Kills a "we" and switches to imperative tense. I noticed a couple
> other "we"s in the previous patches, but this crossed my threshold to
> make a comment.
> 
/me nods. Will fix.

>> only the tail pages subsections, while letting the head page PFN remain
>> different. This presumes that the backing page structs are compound
>> pages, such as the case for compound pagemaps (i.e. ZONE_DEVICE with
>> PGMAP_COMPOUND set)
>>
>> On 2M compound pagemaps, it lets us save 6 pages out of the 8 necessary
> 
> s/lets us save/saves/
> 
Will fix.

>> PFNs necessary
> 
> s/8 necessary PFNs necessary/8 PFNs necessary/

Will fix.

> 
>> to describe the subsection's 32K struct pages we are
>> onlining.
> 
> s/we are onlining/being mapped/
> 
> ...because ZONE_DEVICE pages are never "onlined".
> 
>> On a 1G compound pagemap it let us save 4096 pages.
> 
> s/lets us save/saves/
> 

Will fix both.

>>
>> Sections are 128M (or bigger/smaller),
> 
> Huh?
> 

Section size is arch-dependent if we are being hollistic.
On x86 it's 64M, 128M or 512M right?

 #ifdef CONFIG_X86_32
 # ifdef CONFIG_X86_PAE
 #  define SECTION_SIZE_BITS     29
 #  define MAX_PHYSMEM_BITS      36
 # else
 #  define SECTION_SIZE_BITS     26
 #  define MAX_PHYSMEM_BITS      32
 # endif
 #else /* CONFIG_X86_32 */
 # define SECTION_SIZE_BITS      27 /* matt - 128 is convenient right now */
 # define MAX_PHYSMEM_BITS       (pgtable_l5_enabled() ? 52 : 46)
 #endif

Also, me pointing about section sizes, is because a 1GB+ page vmemmap population will
cross sections in how sparsemem populates the vmemmap. And on that case we gotta reuse the
the PTE/PMD pages across multiple invocations of vmemmap_populate_basepages(). Either
that, or looking at the previous page PTE, but that might be ineficient.

>> @@ -229,38 +235,95 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
>>         for (; addr < end; addr += PAGE_SIZE) {
>>                 pgd = vmemmap_pgd_populate(addr, node);
>>                 if (!pgd)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 p4d = vmemmap_p4d_populate(pgd, addr, node);
>>                 if (!p4d)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 pud = vmemmap_pud_populate(p4d, addr, node);
>>                 if (!pud)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 pmd = vmemmap_pmd_populate(pud, addr, node);
>>                 if (!pmd)
>> -                       return -ENOMEM;
>> -               pte = vmemmap_pte_populate(pmd, addr, node, altmap);
>> +                       return NULL;
>> +               pte = vmemmap_pte_populate(pmd, addr, node, altmap, block);
>>                 if (!pte)
>> -                       return -ENOMEM;
>> +                       return NULL;
>>                 vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
>>         }
>>
>> +       return __va(__pfn_to_phys(pte_pfn(*pte)));
>> +}
>> +
>> +int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
>> +                                        int node, struct vmem_altmap *altmap)
>> +{
>> +       if (!__vmemmap_populate_basepages(start, end, node, altmap, NULL))
>> +               return -ENOMEM;
>>         return 0;
>>  }
>>
>> +static struct page * __meminit vmemmap_populate_reuse(unsigned long start,
>> +                                       unsigned long end, int node,
>> +                                       struct vmem_context *ctx)
>> +{
>> +       unsigned long size, addr = start;
>> +       unsigned long psize = PHYS_PFN(ctx->align) * sizeof(struct page);
>> +
>> +       size = min(psize, end - start);
>> +
>> +       for (; addr < end; addr += size) {
>> +               unsigned long head = addr + PAGE_SIZE;
>> +               unsigned long tail = addr;
>> +               unsigned long last = addr + size;
>> +               void *area;
>> +
>> +               if (ctx->block_page &&
>> +                   IS_ALIGNED((addr - ctx->block_page), psize))
>> +                       ctx->block = NULL;
>> +
>> +               area  = ctx->block;
>> +               if (!area) {
>> +                       if (!__vmemmap_populate_basepages(addr, head, node,
>> +                                                         ctx->altmap, NULL))
>> +                               return NULL;
>> +
>> +                       tail = head + PAGE_SIZE;
>> +                       area = __vmemmap_populate_basepages(head, tail, node,
>> +                                                           ctx->altmap, NULL);
>> +                       if (!area)
>> +                               return NULL;
>> +
>> +                       ctx->block = area;
>> +                       ctx->block_page = addr;
>> +               }
>> +
>> +               if (!__vmemmap_populate_basepages(tail, last, node,
>> +                                                 ctx->altmap, area))
>> +                       return NULL;
>> +       }
> 
> I think that compound page accounting and combined altmap accounting
> makes this difficult to read, and I think the compound page case
> deserves it's own first class loop rather than reusing
> vmemmap_populate_basepages(). With the suggestion to drop altmap
> support I'd expect a vmmemap_populate_compound that takes a compound
> page size and goes the right think with respect to mapping all the
> tail pages to the same pfn.
> 
I can move this to a separate loop as suggested.

But to be able to map all tail pages in one call of vmemmap_populate_compound()
this might requires changes in sparsemem generic code that I am not so sure
they are warranted the added complexity. Otherwise I'll have to probably keep
this logic of @ctx to be able to pass the page to be reused (i.e. @block and
@block_page). That's actually the main reason that made me introduce
a struct vmem_context.


  reply	other threads:[~2021-02-22 11:42 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 compound pagemaps 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 [this message]
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
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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