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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 0/9] mm, sparse-vmemmap: Introduce compound pagemaps
Date: Mon, 22 Feb 2021 11:06:57 +0000	[thread overview]
Message-ID: <ca888299-c576-567b-e6c3-5df3bcd8ca51@oracle.com> (raw)
In-Reply-To: <CAPcyv4gQQ03-nhBNwLK6KDc953SVD1rOs7HFBo_Mu9LFTkXRgw@mail.gmail.com>

On 2/20/21 1:18 AM, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> The link above describes it quite nicely, but the idea is to reuse tail
>> page vmemmap areas, particular the area which only describes tail pages.
>> So a vmemmap page describes 64 struct pages, and the first page for a given
>> ZONE_DEVICE vmemmap would contain the head page and 63 tail pages. The second
>> vmemmap page would contain only tail pages, and that's what gets reused across
>> the rest of the subsection/section. The bigger the page size, the bigger the
>> savings (2M hpage -> save 6 vmemmap pages; 1G hpage -> save 4094 vmemmap pages).
>>
>> In terms of savings, per 1Tb of memory, the struct page cost would go down
>> with compound pagemap:
>>
>> * with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of total memory)
>> * with 1G pages we lose 8MB instead of 16G (0.0007% instead of 1.5% of total memory)
> 
> Nice!
> 

I failed to mention this in the cover letter but I should say that with this trick we will
need to build the vmemmap page tables with basepages for 2M align, as opposed to hugepages
in the vmemmap page tables (as you probably could tell from the patches). This means that
we have to allocate a PMD page, and that costs 2GB per 1Tb (as opposed to 4M). This is
fixable for 1G align by reusing PMD pages (albeit I haven't done that in this RFC series).

The footprint reduction is still big, so to iterate the numbers above (and I will fix this
in the v2 cover letter):

* with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of total memory)
* with 1G pages we lose 8MB instead of 16G (0.0007% instead of 1.5% of total memory)

For vmemmap page tables, we need to use base pages for 2M pages. So taking that into
account, in this RFC series:

* with 2M pages we lose 6G instead of 16G (0.586% instead of 1.5% of total memory)
* with 1G pages we lose ~2GB instead of 16G (0.19% instead of 1.5% of total memory)

For 1G align, we are able to reuse vmemmap PMDs that only point to tail pages, so
ultimately we can get the page table overhead from 2GB to 12MB:

* with 1G pages we lose 20MB instead of 16G (0.0019% instead of 1.5% of total memory)

>>
>> The RDMA patch (patch 8/9) is to demonstrate the improvement for an existing
>> user. For unpin_user_pages() we have an additional test to demonstrate the
>> improvement.  The test performs MR reg/unreg continuously and measuring its
>> rate for a given period. So essentially ib_mem_get and ib_mem_release being
>> stress tested which at the end of day means: pin_user_pages_longterm() and
>> unpin_user_pages() for a scatterlist:
>>
>>     Before:
>>     159 rounds in 5.027 sec: 31617.923 usec / round (device-dax)
>>     466 rounds in 5.009 sec: 10748.456 usec / round (hugetlbfs)
>>
>>     After:
>>     305 rounds in 5.010 sec: 16426.047 usec / round (device-dax)
>>     1073 rounds in 5.004 sec: 4663.622 usec / round (hugetlbfs)
> 
> Why does hugetlbfs get faster for a ZONE_DEVICE change? Might answer
> that question myself when I get to patch 8.
> 
Because the unpinning improvements aren't ZONE_DEVICE specific.

FWIW, I moved those two offending patches outside of this series:

  https://lore.kernel.org/linux-mm/20210212130843.13865-1-joao.m.martins@oracle.com/

>>
>> Patch 9: Improves {pin,get}_user_pages() and its longterm counterpart. It
>> is very experimental, and I imported most of follow_hugetlb_page(), except
>> that we do the same trick as gup-fast. In doing the patch I feel this batching
>> should live in follow_page_mask() and having that being changed to return a set
>> of pages/something-else when walking over PMD/PUDs for THP / devmap pages. This
>> patch then brings the previous test of mr reg/unreg (above) on parity
>> between device-dax and hugetlbfs.
>>
>> Some of the patches are a little fresh/WIP (specially patch 3 and 9) and we are
>> still running tests. Hence the RFC, asking for comments and general direction
>> of the work before continuing.
> 
> Will go look at the code, but I don't see anything scary conceptually
> here. The fact that pfn_to_page() does not need to change is among the
> most compelling features of this approach.
> 
Glad to hear that :D
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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 0/9] mm, sparse-vmemmap: Introduce compound pagemaps
Date: Mon, 22 Feb 2021 11:06:57 +0000	[thread overview]
Message-ID: <ca888299-c576-567b-e6c3-5df3bcd8ca51@oracle.com> (raw)
In-Reply-To: <CAPcyv4gQQ03-nhBNwLK6KDc953SVD1rOs7HFBo_Mu9LFTkXRgw@mail.gmail.com>

On 2/20/21 1:18 AM, Dan Williams wrote:
> On Tue, Dec 8, 2020 at 9:32 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> The link above describes it quite nicely, but the idea is to reuse tail
>> page vmemmap areas, particular the area which only describes tail pages.
>> So a vmemmap page describes 64 struct pages, and the first page for a given
>> ZONE_DEVICE vmemmap would contain the head page and 63 tail pages. The second
>> vmemmap page would contain only tail pages, and that's what gets reused across
>> the rest of the subsection/section. The bigger the page size, the bigger the
>> savings (2M hpage -> save 6 vmemmap pages; 1G hpage -> save 4094 vmemmap pages).
>>
>> In terms of savings, per 1Tb of memory, the struct page cost would go down
>> with compound pagemap:
>>
>> * with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of total memory)
>> * with 1G pages we lose 8MB instead of 16G (0.0007% instead of 1.5% of total memory)
> 
> Nice!
> 

I failed to mention this in the cover letter but I should say that with this trick we will
need to build the vmemmap page tables with basepages for 2M align, as opposed to hugepages
in the vmemmap page tables (as you probably could tell from the patches). This means that
we have to allocate a PMD page, and that costs 2GB per 1Tb (as opposed to 4M). This is
fixable for 1G align by reusing PMD pages (albeit I haven't done that in this RFC series).

The footprint reduction is still big, so to iterate the numbers above (and I will fix this
in the v2 cover letter):

* with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of total memory)
* with 1G pages we lose 8MB instead of 16G (0.0007% instead of 1.5% of total memory)

For vmemmap page tables, we need to use base pages for 2M pages. So taking that into
account, in this RFC series:

* with 2M pages we lose 6G instead of 16G (0.586% instead of 1.5% of total memory)
* with 1G pages we lose ~2GB instead of 16G (0.19% instead of 1.5% of total memory)

For 1G align, we are able to reuse vmemmap PMDs that only point to tail pages, so
ultimately we can get the page table overhead from 2GB to 12MB:

* with 1G pages we lose 20MB instead of 16G (0.0019% instead of 1.5% of total memory)

>>
>> The RDMA patch (patch 8/9) is to demonstrate the improvement for an existing
>> user. For unpin_user_pages() we have an additional test to demonstrate the
>> improvement.  The test performs MR reg/unreg continuously and measuring its
>> rate for a given period. So essentially ib_mem_get and ib_mem_release being
>> stress tested which at the end of day means: pin_user_pages_longterm() and
>> unpin_user_pages() for a scatterlist:
>>
>>     Before:
>>     159 rounds in 5.027 sec: 31617.923 usec / round (device-dax)
>>     466 rounds in 5.009 sec: 10748.456 usec / round (hugetlbfs)
>>
>>     After:
>>     305 rounds in 5.010 sec: 16426.047 usec / round (device-dax)
>>     1073 rounds in 5.004 sec: 4663.622 usec / round (hugetlbfs)
> 
> Why does hugetlbfs get faster for a ZONE_DEVICE change? Might answer
> that question myself when I get to patch 8.
> 
Because the unpinning improvements aren't ZONE_DEVICE specific.

FWIW, I moved those two offending patches outside of this series:

  https://lore.kernel.org/linux-mm/20210212130843.13865-1-joao.m.martins@oracle.com/

>>
>> Patch 9: Improves {pin,get}_user_pages() and its longterm counterpart. It
>> is very experimental, and I imported most of follow_hugetlb_page(), except
>> that we do the same trick as gup-fast. In doing the patch I feel this batching
>> should live in follow_page_mask() and having that being changed to return a set
>> of pages/something-else when walking over PMD/PUDs for THP / devmap pages. This
>> patch then brings the previous test of mr reg/unreg (above) on parity
>> between device-dax and hugetlbfs.
>>
>> Some of the patches are a little fresh/WIP (specially patch 3 and 9) and we are
>> still running tests. Hence the RFC, asking for comments and general direction
>> of the work before continuing.
> 
> Will go look at the code, but I don't see anything scary conceptually
> here. The fact that pfn_to_page() does not need to change is among the
> most compelling features of this approach.
> 
Glad to hear that :D


  reply	other threads:[~2021-02-22 11:07 UTC|newest]

Thread overview: 147+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 17:28 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
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 [this message]
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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