From: Joao Martins <joao.m.martins@oracle.com> To: Jason Gunthorpe <jgg@ziepe.ca> Cc: linux-mm@kvack.org, Dan Williams <dan.j.williams@intel.com>, Ira Weiny <ira.weiny@intel.com>, linux-nvdimm@lists.01.org, Matthew Wilcox <willy@infradead.org>, 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 6/9] mm/gup: Grab head page refcount once for group of subpages Date: Wed, 9 Dec 2020 11:05:39 +0000 [thread overview] Message-ID: <b7f5fe44-f2f5-aea6-57b3-7e14a9ef624d@oracle.com> (raw) In-Reply-To: <20201208194905.GQ5487@ziepe.ca> On 12/8/20 7:49 PM, Jason Gunthorpe wrote: > On Tue, Dec 08, 2020 at 05:28:58PM +0000, Joao Martins wrote: >> Much like hugetlbfs or THPs, we treat device pagemaps with >> compound pages like the rest of GUP handling of compound pages. >> >> Rather than incrementing the refcount every 4K, we record >> all sub pages and increment by @refs amount *once*. >> >> Performance measured by gup_benchmark improves considerably >> get_user_pages_fast() and pin_user_pages_fast(): >> >> $ gup_benchmark -f /dev/dax0.2 -m 16384 -r 10 -S [-u,-a] -n 512 -w >> >> (get_user_pages_fast 2M pages) ~75k us -> ~3.6k us >> (pin_user_pages_fast 2M pages) ~125k us -> ~3.8k us >> >> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> >> mm/gup.c | 67 ++++++++++++++++++++++++++++++++++++++++++-------------- >> 1 file changed, 51 insertions(+), 16 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index 98eb8e6d2609..194e6981eb03 100644 >> +++ b/mm/gup.c >> @@ -2250,22 +2250,68 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, >> } >> #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */ >> >> + >> +static int record_subpages(struct page *page, unsigned long addr, >> + unsigned long end, struct page **pages) >> +{ >> + int nr; >> + >> + for (nr = 0; addr != end; addr += PAGE_SIZE) >> + pages[nr++] = page++; >> + >> + return nr; >> +} >> + >> #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE) >> -static int __gup_device_huge(unsigned long pfn, unsigned long addr, >> - unsigned long end, unsigned int flags, >> - struct page **pages, int *nr) >> +static int __gup_device_compound_huge(struct dev_pagemap *pgmap, >> + struct page *head, unsigned long sz, >> + unsigned long addr, unsigned long end, >> + unsigned int flags, struct page **pages) >> +{ >> + struct page *page; >> + int refs; >> + >> + if (!(pgmap->flags & PGMAP_COMPOUND)) >> + return -1; >> + >> + page = head + ((addr & (sz-1)) >> PAGE_SHIFT); > > All the places that call record_subpages do some kind of maths like > this, it should be placed inside record_subpages and not opencoded > everywhere. > Makes sense. >> + refs = record_subpages(page, addr, end, pages); >> + >> + SetPageReferenced(page); >> + head = try_grab_compound_head(head, refs, flags); >> + if (!head) { >> + ClearPageReferenced(page); >> + return 0; >> + } >> + >> + return refs; >> +} > > Why is all of this special? Any time we see a PMD/PGD/etc pointing to > PFN we can apply this optimization. How come device has its own > special path to do this?? > I think the reason is that zone_device struct pages have no relationship to one other. So you anyways need to change individual pages, as opposed to just the head page. I made it special to avoid breaking other ZONE_DEVICE users (and gating that with PGMAP_COMPOUND). But if there's no concerns with that, I can unilaterally enable it. > Why do we need to check PGMAP_COMPOUND? Why do we need to get pgmap? > (We already removed that from the hmm version of this, was that wrong? > Is this different?) Dan? > > Also undo_dev_pagemap() is now out of date, we have unpin_user_pages() > for that and no other error unwind touches ClearPageReferenced.. > /me nods Yeap I saw that too. > Basic idea is good though! > Cool, thanks! Joao
next prev parent reply other threads:[~2020-12-09 11:05 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 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 [this message] 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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