From: Joao Martins <email@example.com> To: Matthew Wilcox <firstname.lastname@example.org>, John Hubbard <email@example.com> Cc: firstname.lastname@example.org, Dan Williams <email@example.com>, Ira Weiny <firstname.lastname@example.org>, email@example.com, Jason Gunthorpe <firstname.lastname@example.org>, Jane Chu <email@example.com>, Muchun Song <firstname.lastname@example.org>, Mike Kravetz <email@example.com>, Andrew Morton <firstname.lastname@example.org> Subject: Re: [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Date: Wed, 9 Dec 2020 13:12:57 +0000 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20201209063350.GO7338@casper.infradead.org> On 12/9/20 6:33 AM, Matthew Wilcox wrote: > 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 >> Ugh. Yeah will fix. >>> 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? > Nop, my previous text was broken. > 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. > Thanks, I will use this instead. >>> 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.) >> Indeed one could use range_len() / pgmap->align and it would work. But (...) >> 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. :) >> My use of pfns to calculate the nr of pages was to remain consistent with the rest of the code in the function taking references in the pgmap->ref. The usages one sees ofrange_len are are when the hotplug takes place which work at addresses and not PFNs. >> 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. > If possible I would rather keep the pfns as with the rest of the code. Another alternative is like a range_nr_pages helper but I am not sure it's worth the trouble for one caller. Joao
next prev parent reply other threads:[~2020-12-09 13:15 UTC|newest] Thread overview: 80+ 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 [this message] 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 2020-12-08 19:49 ` Jason Gunthorpe 2020-12-09 11:05 ` Joao Martins 2020-12-09 15:15 ` Jason Gunthorpe 2020-12-09 16:02 ` Joao Martins 2020-12-09 16:24 ` Jason Gunthorpe 2020-12-09 17:27 ` Joao Martins 2020-12-09 18:14 ` Matthew Wilcox 2020-12-09 19:08 ` Jason Gunthorpe 2020-12-10 15:43 ` Joao Martins 2020-12-09 4:40 ` John Hubbard 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 19:34 ` Jason Gunthorpe 2020-12-09 5:06 ` John Hubbard 2020-12-09 13:43 ` Jason Gunthorpe 2020-12-09 12:17 ` Joao Martins 2020-12-17 19:05 ` Joao Martins 2020-12-17 20:05 ` Jason Gunthorpe 2020-12-17 22:34 ` Joao Martins 2020-12-18 14:25 ` Jason Gunthorpe 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 2020-12-08 19:29 ` Jason Gunthorpe 2020-12-09 10:59 ` Joao Martins 2020-12-19 13:15 ` Joao Martins 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 19:57 ` Jason Gunthorpe 2020-12-09 8:05 ` Christoph Hellwig 2020-12-09 11:19 ` Joao Martins 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 9:52 ` [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 2021-02-23 18:54 ` Jason Gunthorpe 2021-02-23 22:48 ` Dan Williams 2021-02-23 23:07 ` Jason Gunthorpe 2021-02-24 0:14 ` Dan Williams 2021-02-24 1:00 ` Jason Gunthorpe 2021-02-24 1:32 ` Dan Williams
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