From: John Hubbard <jhubbard@nvidia.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>, Jane Chu <jane.chu@oracle.com>,
Muchun Song" <songmuchun@bytedance.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Andrew@ml01.01.org
Subject: Re: [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages
Date: Tue, 8 Dec 2020 20:40:19 -0800 [thread overview]
Message-ID: <6f729802-1e93-3036-3dba-be35e06af579@nvidia.com> (raw)
In-Reply-To: <20201208172901.17384-8-joao.m.martins@oracle.com>
On 12/8/20 9:28 AM, 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
"gup_test", now that you're in linux-next, actually.
(Maybe I'll retrofit that test with getopt_long(), those options are
getting more elaborate.)
>
> (get_user_pages_fast 2M pages) ~75k us -> ~3.6k us
> (pin_user_pages_fast 2M pages) ~125k us -> ~3.8k us
That is a beautiful result! I'm very motivated to see if this patchset
can make it in, in some form.
>
> 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
> --- a/mm/gup.c
> +++ 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,
If this variable survives (I see Jason requested a reorg of this math stuff,
and I also like that idea), then I'd like a slightly better name for "sz".
I was going to suggest one, but then realized that I can't understand how this
works. See below...
> + unsigned long addr, unsigned long end,
> + unsigned int flags, struct page **pages)
> +{
> + struct page *page;
> + int refs;
> +
> + if (!(pgmap->flags & PGMAP_COMPOUND))
> + return -1;
btw, I'm unhappy with returning -1 here and assigning it later to a refs variable.
(And that will show up even more clearly as an issue if you attempt to make
refs unsigned everywhere!)
I'm not going to suggest anything because there are a lot of ways to structure
these routines, and I don't want to overly constrain you. Just please don't assign
negative values to any refs variables.
> +
> + page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
If you pass in PMD_SHIFT or PUD_SHIFT for, that's a number-of-bits, isn't it?
Not a size. And if it's not a size, then sz - 1 doesn't work, does it? If it
does work, then better naming might help. I'm probably missing a really
obvious math trick here.
thanks,
--
John Hubbard
NVIDIA
> + 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;
> +}
> +
> +static int __gup_device_huge(unsigned long pfn, unsigned long sz,
> + unsigned long addr, unsigned long end,
> + unsigned int flags, struct page **pages, int *nr)
> {
> int nr_start = *nr;
> struct dev_pagemap *pgmap = NULL;
>
> do {
> struct page *page = pfn_to_page(pfn);
> + int refs;
>
> pgmap = get_dev_pagemap(pfn, pgmap);
> if (unlikely(!pgmap)) {
> undo_dev_pagemap(nr, nr_start, flags, pages);
> return 0;
> }
> +
> + refs = __gup_device_compound_huge(pgmap, page, sz, addr, end,
> + flags, pages + *nr);
> + if (refs >= 0) {
> + *nr += refs;
> + put_dev_pagemap(pgmap);
> + return refs ? 1 : 0;
> + }
> +
> SetPageReferenced(page);
> pages[*nr] = page;
> if (unlikely(!try_grab_page(page, flags))) {
> @@ -2289,7 +2335,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> int nr_start = *nr;
>
> fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
> + if (!__gup_device_huge(fault_pfn, PMD_SHIFT, addr, end, flags, pages, nr))
> return 0;
>
> if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> @@ -2307,7 +2353,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> int nr_start = *nr;
>
> fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> - if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
> + if (!__gup_device_huge(fault_pfn, PUD_SHIFT, addr, end, flags, pages, nr))
> return 0;
>
> if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> @@ -2334,17 +2380,6 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
> }
> #endif
>
> -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;
> -}
> -
> #ifdef CONFIG_ARCH_HAS_HUGEPD
> static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
> unsigned long sz)
>
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next prev parent reply other threads:[~2020-12-09 4:40 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 [this message]
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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