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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 14:32:04 +0000	[thread overview]
Message-ID: <872eec38-3c18-72dd-c5c6-147c02ae33d1@oracle.com> (raw)
In-Reply-To: <ca888299-c576-567b-e6c3-5df3bcd8ca51@oracle.com>



On 2/22/21 11:06 AM, Joao Martins wrote:
> 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). 

Also to be clear: by "we will need to build the vmemmap page tables with basepages for 2M
align" I strictly refer to the ZONE_DEVICE range we are mapping the struct pages. It's not
the enterity of the vmemmap!

> 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 14:32:04 +0000	[thread overview]
Message-ID: <872eec38-3c18-72dd-c5c6-147c02ae33d1@oracle.com> (raw)
In-Reply-To: <ca888299-c576-567b-e6c3-5df3bcd8ca51@oracle.com>



On 2/22/21 11:06 AM, Joao Martins wrote:
> 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). 

Also to be clear: by "we will need to build the vmemmap page tables with basepages for 2M
align" I strictly refer to the ZONE_DEVICE range we are mapping the struct pages. It's not
the enterity of the vmemmap!

> 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 14:32 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
2021-02-22 11:06     ` Joao Martins
2021-02-22 14:32     ` Joao Martins [this message]
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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