From: David Hildenbrand <david@redhat.com>
To: Joao Martins <joao.m.martins@oracle.com>, linux-mm@kvack.org
Cc: 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: Wed, 9 Dec 2020 10:38:56 +0100 [thread overview]
Message-ID: <3d6923af-2684-cbdc-928c-2d849cc2062b@redhat.com> (raw)
In-Reply-To: <20201208172901.17384-1-joao.m.martins@oracle.com>
On 08.12.20 18:28, Joao Martins wrote:
> Hey,
>
> This small series, attempts at minimizing 'struct page' overhead by
> pursuing a similar approach as Muchun Song series "Free some vmemmap
> pages of hugetlb page"[0] but applied to devmap/ZONE_DEVICE.
>
> [0] https://lore.kernel.org/linux-mm/20201130151838.11208-1-songmuchun@bytedance.com/
>
> 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)
>
That's the dream :)
> Along the way I've extended it past 'struct page' overhead *trying* to address a
> few performance issues we knew about for pmem, specifically on the
> {pin,get}_user_pages* function family with device-dax vmas which are really
> slow even of the fast variants. THP is great on -fast variants but all except
> hugetlbfs perform rather poorly on non-fast gup.
>
> So to summarize what the series does:
>
> Patches 1-5: Much like Muchun series, we reuse tail page areas across a given
> page size (namely @align was referred by remaining memremap/dax code) and
> enabling of memremap to initialize the ZONE_DEVICE pages as compound pages or a
> given @align order. The main difference though, is that contrary to the hugetlbfs
> series, there's no vmemmap for the area, because we are onlining it.
Yeah, I'd argue that this case is a lot easier to handle. When the buddy
is involved, things get more complicated.
--
Thanks,
David / dhildenb
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next prev parent reply other threads:[~2020-12-09 9:39 UTC|newest]
Thread overview: 67+ 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 ` [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Joao Martins
2020-12-09 5:59 ` John Hubbard
2020-12-09 6:33 ` Matthew Wilcox
2020-12-09 13:12 ` Joao Martins
2021-02-20 1:43 ` Dan Williams
2021-02-22 11:24 ` Joao Martins
2021-02-22 20:37 ` Dan Williams
2021-02-23 15:46 ` Joao Martins
2021-02-23 16:50 ` Dan Williams
2021-02-23 17:18 ` Joao Martins
2021-02-23 18:18 ` Dan Williams
2021-03-10 18:12 ` Joao Martins
2021-03-12 5:54 ` Dan Williams
2021-02-20 1:24 ` Dan Williams
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
2020-12-09 6:16 ` John Hubbard
2020-12-09 13:51 ` Joao Martins
2021-02-20 1:49 ` Dan Williams
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 17:38 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size Joao Martins
2021-02-20 3:34 ` Dan Williams
2021-02-22 11:42 ` Joao Martins
2021-02-22 22:40 ` Dan Williams
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
2021-02-20 6:17 ` Dan Williams
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 ` [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages Joao Martins
2020-12-09 4:40 ` John Hubbard
2020-12-09 13:44 ` Joao Martins
[not found] ` <20201208194905.GQ5487@ziepe.ca>
2020-12-09 11:05 ` Joao Martins
[not found] ` <20201209151505.GV5487@ziepe.ca>
2020-12-09 16:02 ` Joao Martins
[not found] ` <20201209162438.GW5487@ziepe.ca>
2020-12-09 17:27 ` Joao Martins
2020-12-09 18:14 ` Matthew Wilcox
2020-12-10 15:43 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 7/9] mm/gup: Decrement head page " Joao Martins
[not found] ` <20201208193446.GP5487@ziepe.ca>
2020-12-09 5:06 ` John Hubbard
2020-12-09 12:17 ` Joao Martins
2020-12-17 19:05 ` Joao Martins
[not found] ` <20201217200530.GK5487@ziepe.ca>
2020-12-17 22:34 ` Joao Martins
2020-12-19 2:06 ` John Hubbard
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
2020-12-09 5:18 ` John Hubbard
[not found] ` <20201208192935.GA1908088@ziepe.ca>
2020-12-09 10:59 ` Joao Martins
2020-12-19 13:15 ` Joao Martins
2020-12-08 17:29 ` [PATCH RFC 9/9] mm: Add follow_devmap_page() for devdax vmas Joao Martins
2020-12-09 5:23 ` John Hubbard
[not found] ` <20201208195754.GR5487@ziepe.ca>
2020-12-09 8:05 ` Christoph Hellwig
2020-12-09 11:19 ` Joao Martins
2020-12-09 9:38 ` David Hildenbrand [this message]
2020-12-09 9:52 ` [External] [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps Muchun Song
2021-02-20 1:18 ` Dan Williams
2021-02-22 11:06 ` Joao Martins
2021-02-22 14:32 ` Joao Martins
2021-02-23 16:28 ` Joao Martins
2021-02-23 16:44 ` Dan Williams
2021-02-23 17:15 ` Joao Martins
2021-02-23 18:15 ` Dan Williams
[not found] ` <20210223185435.GO2643399@ziepe.ca>
2021-02-23 22:48 ` Dan Williams
[not found] ` <20210223230723.GP2643399@ziepe.ca>
2021-02-24 0:14 ` Dan Williams
[not found] ` <20210224010017.GQ2643399@ziepe.ca>
2021-02-24 1:32 ` Dan Williams
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