mm: introduce vm_ops->map_pages()
Here's new version of faultaround patchset. It took a while to tune it and collect performance data. First patch adds new callback ->map_pages to vm_operations_struct. ->map_pages() is called when VM asks to map easy accessible pages. Filesystem should find and map pages associated with offsets from "pgoff" till "max_pgoff". ->map_pages() is called with page table locked and must not block. If it's not possible to reach a page without blocking, filesystem should skip it. Filesystem should use do_set_pte() to setup page table entry. Pointer to entry associated with offset "pgoff" is passed in "pte" field in vm_fault structure. Pointers to entries for other offsets should be calculated relative to "pte". Currently VM use ->map_pages only on read page fault path. We try to map FAULT_AROUND_PAGES a time. FAULT_AROUND_PAGES is 16 for now. Performance data for different FAULT_AROUND_ORDER is below. TODO: - implement ->map_pages() for shmem/tmpfs; - modify get_user_pages() to be able to use ->map_pages() and implement mmap(MAP_POPULATE|MAP_NONBLOCK) on top. ========================================================================= Tested on 4-socket machine (120 threads) with 128GiB of RAM. Few real-world workloads. The sweet spot for FAULT_AROUND_ORDER here is somewhere between 3 and 5. Let's say 4 :) Linux build (make -j60) FAULT_AROUND_ORDER Baseline 1 3 4 5 7 9 minor-faults 283,301,572 247,151,987 212,215,789 204,772,882 199,568,944 194,703,779 193,381,485 time, seconds 151.227629483 153.920996480 151.356125472 150.863792049 150.879207877 151.150764954 151.450962358 Linux rebuild (make -j60) FAULT_AROUND_ORDER Baseline 1 3 4 5 7 9 minor-faults 5,396,854 4,148,444 2,855,286 2,577,282 2,361,957 2,169,573 2,112,643 time, seconds 27.404543757 27.559725591 27.030057426 26.855045126 26.678618635 26.974523490 26.761320095 Git test suite (make -j60 test) FAULT_AROUND_ORDER Baseline 1 3 4 5 7 9 minor-faults 129,591,823 99,200,751 66,106,718 57,606,410 51,510,808 45,776,813 44,085,515 time, seconds 66.087215026 64.784546905 64.401156567 65.282708668 66.034016829 66.793780811 67.237810413 Two synthetic tests: access every word in file in sequential/random order. It doesn't improve much after FAULT_AROUND_ORDER == 4. Sequential access 16GiB file FAULT_AROUND_ORDER Baseline 1 3 4 5 7 9 1 thread minor-faults 4,195,437 2,098,275 525,068 262,251 131,170 32,856 8,282 time, seconds 7.250461742 6.461711074 5.493859139 5.488488147 5.707213983 5.898510832 5.109232856 8 threads minor-faults 33,557,540 16,892,728 4,515,848 2,366,999 1,423,382 442,732 142,339 time, seconds 16.649304881 9.312555263 6.612490639 6.394316732 6.669827501 6.75078944 6.371900528 32 threads minor-faults 134,228,222 67,526,810 17,725,386 9,716,537 4,763,731 1,668,921 537,200 time, seconds 49.164430543 29.712060103 12.938649729 10.175151004 11.840094583 9.594081325 9.928461797 60 threads minor-faults 251,687,988 126,146,952 32,919,406 18,208,804 10,458,947 2,733,907 928,217 time, seconds 86.260656897 49.626551828 22.335007632 17.608243696 16.523119035 16.339489186 16.326390902 120 threads minor-faults 503,352,863 252,939,677 67,039,168 35,191,827 19,170,091 4,688,357 1,471,862 time, seconds 124.589206333 79.757867787 39.508707872 32.167281632 29.972989292 28.729834575 28.042251622 Random access 1GiB file 1 thread minor-faults 262,636 132,743 34,369 17,299 8,527 3,451 1,222 time, seconds 15.351890914 16.613802482 16.569227308 15.179220992 16.557356122 16.578247824 15.365266994 8 threads minor-faults 2,098,948 1,061,871 273,690 154,501 87,110 25,663 7,384 time, seconds 15.040026343 15.096933500 14.474757288 14.289129964 14.411537468 14.296316837 14.395635804 32 threads minor-faults 8,390,734 4,231,023 1,054,432 528,847 269,242 97,746 26,881 time, seconds 20.430433109 21.585235358 22.115062928 14.872878951 14.880856305 14.883370649 14.821261690 60 threads minor-faults 15,733,258 7,892,809 1,973,393 988,266 594,789 164,994 51,691 time, seconds 26.577302548 25.692397770 18.728863715 20.153026398 21.619101933 17.745086260 17.613215273 120 threads minor-faults 31,471,111 15,816,616 3,959,209 1,978,685 1,008,299 264,635 96,010 time, seconds 41.835322703 40.459786095 36.085306105 35.313894834 35.814445675 36.552633793 34.289210594 Touch only one page in page table in 16GiB file FAULT_AROUND_ORDER Baseline 1 3 4 5 7 9 1 thread minor-faults 8,372 8,324 8,270 8,260 8,249 8,239 8,237 time, seconds 0.039892712 0.045369149 0.051846126 0.063681685 0.079095975 0.17652406 0.541213386 8 threads minor-faults 65,731 65,681 65,628 65,620 65,608 65,599 65,596 time, seconds 0.124159196 0.488600638 0.156854426 0.191901957 0.242631486 0.543569456 1.677303984 32 threads minor-faults 262,388 262,341 262,285 262,276 262,266 262,257 263,183 time, seconds 0.452421421 0.488600638 0.565020946 0.648229739 0.789850823 1.651584361 5.000361559 60 threads minor-faults 491,822 491,792 491,723 491,711 491,701 491,691 491,825 time, seconds 0.763288616 0.869620515 0.980727360 1.161732354 1.466915814 3.04041448 9.308612938 120 threads minor-faults 983,466 983,655 983,366 983,372 983,363 984,083 984,164 time, seconds 1.595846553 1.667902182 2.008959376 2.425380942 2.941368804 5.977807890 18.401846125 This patch (of 2): Introduce new vm_ops callback ->map_pages() and uses it for mapping easy accessible pages around fault address. On read page fault, if filesystem provides ->map_pages(), we try to map up to FAULT_AROUND_PAGES pages around page fault address in hope to reduce number of minor page faults. We call ->map_pages first and use ->fault() as fallback if page by the offset is not ready to be mapped (cold page cache or something). Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Matthew Wilcox <matthew.r.wilcox@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Dave Chinner <david@fromorbit.com> Cc: Ning Qu <quning@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov
Linus Torvalds
parent
179e09637c
commit
8c6e50b029
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@ -529,6 +529,7 @@ locking rules:
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open: yes
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close: yes
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fault: yes can return with page locked
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map_pages: yes
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page_mkwrite: yes can return with page locked
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access: yes
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@ -540,6 +541,15 @@ the page, then ensure it is not already truncated (the page lock will block
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subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
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locked. The VM will unlock the page.
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->map_pages() is called when VM asks to map easy accessible pages.
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Filesystem should find and map pages associated with offsets from "pgoff"
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till "max_pgoff". ->map_pages() is called with page table locked and must
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not block. If it's not possible to reach a page without blocking,
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filesystem should skip it. Filesystem should use do_set_pte() to setup
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page table entry. Pointer to entry associated with offset "pgoff" is
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passed in "pte" field in vm_fault structure. Pointers to entries for other
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offsets should be calculated relative to "pte".
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->page_mkwrite() is called when a previously read-only pte is
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about to become writeable. The filesystem again must ensure that there are
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no truncate/invalidate races, and then return with the page locked. If
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@ -213,6 +213,10 @@ struct vm_fault {
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* is set (which is also implied by
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* VM_FAULT_ERROR).
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*/
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/* for ->map_pages() only */
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pgoff_t max_pgoff; /* map pages for offset from pgoff till
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* max_pgoff inclusive */
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pte_t *pte; /* pte entry associated with ->pgoff */
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};
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/*
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@ -224,6 +228,7 @@ struct vm_operations_struct {
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void (*open)(struct vm_area_struct * area);
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void (*close)(struct vm_area_struct * area);
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int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
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void (*map_pages)(struct vm_area_struct *vma, struct vm_fault *vmf);
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/* notification that a previously read-only page is about to become
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* writable, if an error is returned it will cause a SIGBUS */
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@ -584,6 +589,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
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pte = pte_mkwrite(pte);
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return pte;
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}
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void do_set_pte(struct vm_area_struct *vma, unsigned long address,
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struct page *page, pte_t *pte, bool write, bool anon);
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#endif
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/*
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81
mm/memory.c
81
mm/memory.c
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@ -3342,7 +3342,22 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address,
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return ret;
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}
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static void do_set_pte(struct vm_area_struct *vma, unsigned long address,
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/**
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* do_set_pte - setup new PTE entry for given page and add reverse page mapping.
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*
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* @vma: virtual memory area
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* @address: user virtual address
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* @page: page to map
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* @pte: pointer to target page table entry
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* @write: true, if new entry is writable
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* @anon: true, if it's anonymous page
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*
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* Caller must hold page table lock relevant for @pte.
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*
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* Target users are page handler itself and implementations of
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* vm_ops->map_pages.
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*/
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void do_set_pte(struct vm_area_struct *vma, unsigned long address,
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struct page *page, pte_t *pte, bool write, bool anon)
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{
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pte_t entry;
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@ -3366,6 +3381,52 @@ static void do_set_pte(struct vm_area_struct *vma, unsigned long address,
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update_mmu_cache(vma, address, pte);
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}
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#define FAULT_AROUND_ORDER 4
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#define FAULT_AROUND_PAGES (1UL << FAULT_AROUND_ORDER)
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#define FAULT_AROUND_MASK ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1)
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static void do_fault_around(struct vm_area_struct *vma, unsigned long address,
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pte_t *pte, pgoff_t pgoff, unsigned int flags)
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{
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unsigned long start_addr;
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pgoff_t max_pgoff;
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struct vm_fault vmf;
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int off;
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BUILD_BUG_ON(FAULT_AROUND_PAGES > PTRS_PER_PTE);
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start_addr = max(address & FAULT_AROUND_MASK, vma->vm_start);
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off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
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pte -= off;
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pgoff -= off;
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/*
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* max_pgoff is either end of page table or end of vma
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* or FAULT_AROUND_PAGES from pgoff, depending what is neast.
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*/
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max_pgoff = pgoff - ((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
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PTRS_PER_PTE - 1;
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max_pgoff = min3(max_pgoff, vma_pages(vma) + vma->vm_pgoff - 1,
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pgoff + FAULT_AROUND_PAGES - 1);
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/* Check if it makes any sense to call ->map_pages */
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while (!pte_none(*pte)) {
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if (++pgoff > max_pgoff)
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return;
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start_addr += PAGE_SIZE;
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if (start_addr >= vma->vm_end)
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return;
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pte++;
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}
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vmf.virtual_address = (void __user *) start_addr;
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vmf.pte = pte;
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vmf.pgoff = pgoff;
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vmf.max_pgoff = max_pgoff;
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vmf.flags = flags;
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vma->vm_ops->map_pages(vma, &vmf);
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}
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static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmd,
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pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
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@ -3373,7 +3434,20 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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struct page *fault_page;
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spinlock_t *ptl;
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pte_t *pte;
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int ret;
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int ret = 0;
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/*
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* Let's call ->map_pages() first and use ->fault() as fallback
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* if page by the offset is not ready to be mapped (cold cache or
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* something).
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*/
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if (vma->vm_ops->map_pages) {
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pte = pte_offset_map_lock(mm, pmd, address, &ptl);
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do_fault_around(vma, address, pte, pgoff, flags);
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if (!pte_same(*pte, orig_pte))
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goto unlock_out;
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pte_unmap_unlock(pte, ptl);
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}
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ret = __do_fault(vma, address, pgoff, flags, &fault_page);
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if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
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@ -3387,8 +3461,9 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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return ret;
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}
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do_set_pte(vma, address, fault_page, pte, false, false);
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pte_unmap_unlock(pte, ptl);
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unlock_page(fault_page);
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unlock_out:
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pte_unmap_unlock(pte, ptl);
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return ret;
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}
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