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 9/9] mm: Add follow_devmap_page() for devdax vmas
Date: Tue, 8 Dec 2020 21:23:48 -0800 [thread overview]
Message-ID: <aa624a3d-f760-ddf6-6298-1938e24be842@nvidia.com> (raw)
In-Reply-To: <20201208172901.17384-11-joao.m.martins@oracle.com>
On 12/8/20 9:29 AM, Joao Martins wrote:
> Similar to follow_hugetlb_page() add a follow_devmap_page which rather
> than calling follow_page() per 4K page in a PMD/PUD it does so for the
> entire PMD, where we lock the pmd/pud, get all pages , unlock.
>
> While doing so, we only change the refcount once when PGMAP_COMPOUND is
> passed in.
>
> This let us improve {pin,get}_user_pages{,_longterm}() considerably:
>
> $ gup_benchmark -f /dev/dax0.2 -m 16384 -r 10 -S [-U,-b,-L] -n 512 -w
>
d> (<test>) [before] -> [after]
> (get_user_pages 2M pages) ~150k us -> ~8.9k us
> (pin_user_pages 2M pages) ~192k us -> ~9k us
> (pin_user_pages_longterm 2M pages) ~200k us -> ~19k us
>
Yes, this is a massive improvement.
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
> I've special-cased this to device-dax vmas given its similar page size
> guarantees as hugetlbfs, but I feel this is a bit wrong. I am
> replicating follow_hugetlb_page() as RFC ought to seek feedback whether
> this should be generalized if no fundamental issues exist. In such case,
> should I be changing follow_page_mask() to take either an array of pages
> or a function pointer and opaque arguments which would let caller pick
> its structure?
I don't know which approach is better because I haven't yet attempted to
find the common elements in these routines. But if there is *any way* to
avoid this copy-paste creation of yet more following of pages, then it's
*very* good to do.
thanks,
--
John Hubbard
NVIDIA
> ---
> include/linux/huge_mm.h | 4 +
> include/linux/mm.h | 2 +
> mm/gup.c | 22 ++++-
> mm/huge_memory.c | 202 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 227 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 0365aa97f8e7..da87ecea19e6 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -293,6 +293,10 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
> pmd_t *pmd, int flags, struct dev_pagemap **pgmap);
> struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
> pud_t *pud, int flags, struct dev_pagemap **pgmap);
> +long follow_devmap_page(struct mm_struct *mm, struct vm_area_struct *vma,
> + struct page **pages, struct vm_area_struct **vmas,
> + unsigned long *position, unsigned long *nr_pages,
> + long i, unsigned int flags, int *locked);
>
> extern vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t orig_pmd);
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8b0155441835..466c88679628 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1164,6 +1164,8 @@ static inline void get_page(struct page *page)
> page_ref_inc(page);
> }
>
> +__maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
> + unsigned int flags);
> bool __must_check try_grab_page(struct page *page, unsigned int flags);
>
> static inline __must_check bool try_get_page(struct page *page)
> diff --git a/mm/gup.c b/mm/gup.c
> index 3a9a7229f418..50effb9cc349 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -78,7 +78,7 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
> * considered failure, and furthermore, a likely bug in the caller, so a warning
> * is also emitted.
> */
> -static __maybe_unused struct page *try_grab_compound_head(struct page *page,
> +__maybe_unused struct page *try_grab_compound_head(struct page *page,
> int refs,
> unsigned int flags)
> {
> @@ -880,8 +880,8 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
> * does not include FOLL_NOWAIT, the mmap_lock may be released. If it
> * is, *@locked will be set to 0 and -EBUSY returned.
> */
> -static int faultin_page(struct vm_area_struct *vma,
> - unsigned long address, unsigned int *flags, int *locked)
> +int faultin_page(struct vm_area_struct *vma,
> + unsigned long address, unsigned int *flags, int *locked)
> {
> unsigned int fault_flags = 0;
> vm_fault_t ret;
> @@ -1103,6 +1103,22 @@ static long __get_user_pages(struct mm_struct *mm,
> }
> continue;
> }
> + if (vma_is_dax(vma)) {
> + i = follow_devmap_page(mm, vma, pages, vmas,
> + &start, &nr_pages, i,
> + gup_flags, locked);
> + if (locked && *locked == 0) {
> + /*
> + * We've got a VM_FAULT_RETRY
> + * and we've lost mmap_lock.
> + * We must stop here.
> + */
> + BUG_ON(gup_flags & FOLL_NOWAIT);
> + BUG_ON(ret != 0);
> + goto out;
> + }
> + continue;
> + }
> }
> retry:
> /*
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ec2bb93f7431..20bfbf211dc3 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1168,6 +1168,208 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
> return page;
> }
>
> +long follow_devmap_page(struct mm_struct *mm, struct vm_area_struct *vma,
> + struct page **pages, struct vm_area_struct **vmas,
> + unsigned long *position, unsigned long *nr_pages,
> + long i, unsigned int flags, int *locked)
> +{
> + unsigned long pfn_offset;
> + unsigned long vaddr = *position;
> + unsigned long remainder = *nr_pages;
> + unsigned long align = vma_kernel_pagesize(vma);
> + unsigned long align_nr_pages = align >> PAGE_SHIFT;
> + unsigned long mask = ~(align-1);
> + unsigned long nr_pages_hpage = 0;
> + struct dev_pagemap *pgmap = NULL;
> + int err = -EFAULT;
> +
> + if (align == PAGE_SIZE)
> + return i;
> +
> + while (vaddr < vma->vm_end && remainder) {
> + pte_t *pte;
> + spinlock_t *ptl = NULL;
> + int absent;
> + struct page *page;
> +
> + /*
> + * If we have a pending SIGKILL, don't keep faulting pages and
> + * potentially allocating memory.
> + */
> + if (fatal_signal_pending(current)) {
> + remainder = 0;
> + break;
> + }
> +
> + /*
> + * Some archs (sparc64, sh*) have multiple pte_ts to
> + * each hugepage. We have to make sure we get the
> + * first, for the page indexing below to work.
> + *
> + * Note that page table lock is not held when pte is null.
> + */
> + pte = huge_pte_offset(mm, vaddr & mask, align);
> + if (pte) {
> + if (align == PMD_SIZE)
> + ptl = pmd_lockptr(mm, (pmd_t *) pte);
> + else if (align == PUD_SIZE)
> + ptl = pud_lockptr(mm, (pud_t *) pte);
> + spin_lock(ptl);
> + }
> + absent = !pte || pte_none(ptep_get(pte));
> +
> + if (absent && (flags & FOLL_DUMP)) {
> + if (pte)
> + spin_unlock(ptl);
> + remainder = 0;
> + break;
> + }
> +
> + if (absent ||
> + ((flags & FOLL_WRITE) &&
> + !pte_write(ptep_get(pte)))) {
> + vm_fault_t ret;
> + unsigned int fault_flags = 0;
> +
> + if (pte)
> + spin_unlock(ptl);
> + if (flags & FOLL_WRITE)
> + fault_flags |= FAULT_FLAG_WRITE;
> + if (locked)
> + fault_flags |= FAULT_FLAG_ALLOW_RETRY |
> + FAULT_FLAG_KILLABLE;
> + if (flags & FOLL_NOWAIT)
> + fault_flags |= FAULT_FLAG_ALLOW_RETRY |
> + FAULT_FLAG_RETRY_NOWAIT;
> + if (flags & FOLL_TRIED) {
> + /*
> + * Note: FAULT_FLAG_ALLOW_RETRY and
> + * FAULT_FLAG_TRIED can co-exist
> + */
> + fault_flags |= FAULT_FLAG_TRIED;
> + }
> + ret = handle_mm_fault(vma, vaddr, flags, NULL);
> + if (ret & VM_FAULT_ERROR) {
> + err = vm_fault_to_errno(ret, flags);
> + remainder = 0;
> + break;
> + }
> + if (ret & VM_FAULT_RETRY) {
> + if (locked &&
> + !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
> + *locked = 0;
> + *nr_pages = 0;
> + /*
> + * VM_FAULT_RETRY must not return an
> + * error, it will return zero
> + * instead.
> + *
> + * No need to update "position" as the
> + * caller will not check it after
> + * *nr_pages is set to 0.
> + */
> + return i;
> + }
> + continue;
> + }
> +
> + pfn_offset = (vaddr & ~mask) >> PAGE_SHIFT;
> + page = pte_page(ptep_get(pte));
> +
> + pgmap = get_dev_pagemap(page_to_pfn(page), pgmap);
> + if (!pgmap) {
> + spin_unlock(ptl);
> + remainder = 0;
> + err = -EFAULT;
> + break;
> + }
> +
> + /*
> + * If subpage information not requested, update counters
> + * and skip the same_page loop below.
> + */
> + if (!pages && !vmas && !pfn_offset &&
> + (vaddr + align < vma->vm_end) &&
> + (remainder >= (align_nr_pages))) {
> + vaddr += align;
> + remainder -= align_nr_pages;
> + i += align_nr_pages;
> + spin_unlock(ptl);
> + continue;
> + }
> +
> + nr_pages_hpage = 0;
> +
> +same_page:
> + if (pages) {
> + pages[i] = mem_map_offset(page, pfn_offset);
> +
> + /*
> + * try_grab_page() should always succeed here, because:
> + * a) we hold the ptl lock, and b) we've just checked
> + * that the huge page is present in the page tables.
> + */
> + if (!(pgmap->flags & PGMAP_COMPOUND) &&
> + WARN_ON_ONCE(!try_grab_page(pages[i], flags))) {
> + spin_unlock(ptl);
> + remainder = 0;
> + err = -ENOMEM;
> + break;
> + }
> +
> + }
> +
> + if (vmas)
> + vmas[i] = vma;
> +
> + vaddr += PAGE_SIZE;
> + ++pfn_offset;
> + --remainder;
> + ++i;
> + nr_pages_hpage++;
> + if (vaddr < vma->vm_end && remainder &&
> + pfn_offset < align_nr_pages) {
> + /*
> + * We use pfn_offset to avoid touching the pageframes
> + * of this compound page.
> + */
> + goto same_page;
> + } else {
> + /*
> + * try_grab_compound_head() should always succeed here,
> + * because: a) we hold the ptl lock, and b) we've just
> + * checked that the huge page is present in the page
> + * tables. If the huge page is present, then the tail
> + * pages must also be present. The ptl prevents the
> + * head page and tail pages from being rearranged in
> + * any way. So this page must be available at this
> + * point, unless the page refcount overflowed:
> + */
> + if ((pgmap->flags & PGMAP_COMPOUND) &&
> + WARN_ON_ONCE(!try_grab_compound_head(pages[i-1],
> + nr_pages_hpage,
> + flags))) {
> + put_dev_pagemap(pgmap);
> + spin_unlock(ptl);
> + remainder = 0;
> + err = -ENOMEM;
> + break;
> + }
> + put_dev_pagemap(pgmap);
> + }
> + spin_unlock(ptl);
> + }
> + *nr_pages = remainder;
> + /*
> + * setting position is actually required only if remainder is
> + * not zero but it's faster not to add a "if (remainder)"
> + * branch.
> + */
> + *position = vaddr;
> +
> + return i ? i : err;
> +}
> +
> int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
> struct vm_area_struct *vma)
>
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next prev parent reply other threads:[~2020-12-09 5:23 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 [this message]
[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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