From: Matthew Wilcox <willy@infradead.org>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Joao Martins <joao.m.martins@oracle.com>,
linux-mm@kvack.org, linux-nvdimm@lists.01.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 1/9] memremap: add ZONE_DEVICE support for compound pages
Date: Wed, 9 Dec 2020 06:33:50 +0000 [thread overview]
Message-ID: <20201209063350.GO7338@casper.infradead.org> (raw)
In-Reply-To: <7249cfd2-c178-2e6a-6b03-307a05f11785@nvidia.com>
On Tue, Dec 08, 2020 at 09:59:19PM -0800, John Hubbard wrote:
> On 12/8/20 9:28 AM, Joao Martins wrote:
> > Add a new flag for struct dev_pagemap which designates that a a pagemap
>
> a a
>
> > is described as a set of compound pages or in other words, that how
> > pages are grouped together in the page tables are reflected in how we
> > describe struct pages. This means that rather than initializing
> > individual struct pages, we also initialize these struct pages, as
>
> Let's not say "rather than x, we also do y", because it's self-contradictory.
> I think you want to just leave out the "also", like this:
>
> "This means that rather than initializing> individual struct pages, we
> initialize these struct pages ..."
>
> Is that right?
I'd phrase it as:
Add a new flag for struct dev_pagemap which specifies that a pagemap is
composed of a set of compound pages instead of individual pages. When
these pages are initialised, most are initialised as tail pages
instead of order-0 pages.
> > For certain ZONE_DEVICE users, like device-dax, which have a fixed page
> > size, this creates an opportunity to optimize GUP and GUP-fast walkers,
> > thus playing the same tricks as hugetlb pages.
Rather than "playing the same tricks", how about "are treated the same
way as THP or hugetlb pages"?
> > + if (pgmap->flags & PGMAP_COMPOUND)
> > + percpu_ref_get_many(pgmap->ref, (pfn_end(pgmap, range_id)
> > + - pfn_first(pgmap, range_id)) / PHYS_PFN(pgmap->align));
>
> Is there some reason that we cannot use range_len(), instead of pfn_end() minus
> pfn_first()? (Yes, this more about the pre-existing code than about your change.)
>
> And if not, then why are the nearby range_len() uses OK? I realize that range_len()
> is simpler and skips a case, but it's not clear that it's required here. But I'm
> new to this area so be warned. :)
>
> Also, dividing by PHYS_PFN() feels quite misleading: that function does what you
> happen to want, but is not named accordingly. Can you use or create something
> more accurately named? Like "number of pages in this large page"?
We have compound_nr(), but that takes a struct page as an argument.
We also have HPAGE_NR_PAGES. I'm not quite clear what you want.
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next prev parent reply other threads:[~2020-12-09 6:34 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 [this message]
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 ` [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps David Hildenbrand
2020-12-09 9:52 ` [External] " 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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