The patch titled
Subject: mm: introduce page_needs_cow_for_dma() for deciding whether cow
has been added to the -mm tree. Its filename is
mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm: introduce page_needs_cow_for_dma() for deciding whether cow
We've got quite a few places (pte, pmd, pud) that explicitly checked
against whether we should break the cow right now during fork(). It's
easier to provide a helper, especially before we work the same thing on
hugetlbfs.
Since we'll reference is_cow_mapping() in mm.h, move it there too.
Actually it suites mm.h more since internal.h is mm/ only, but mm.h is
exported to the whole kernel. With that we should expect another patch to
use is_cow_mapping() whenever we can across the kernel since we do use it
quite a lot but it's always done with raw code against VM_* flags.
Link: https://lkml.kernel.org/r/20210217233547.93892-4-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Cc: Gal Pressman <galpress@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Kirill Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Roland Scheidegger <sroland@xxxxxxxxxx>
Cc: VMware Graphics <linux-graphics-maintainer@xxxxxxxxxx>
Cc: Wei Zhang <wzam@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 21 +++++++++++++++++++++
mm/huge_memory.c | 8 ++------
mm/internal.h | 5 -----
mm/memory.c | 8 +-------
4 files changed, 24 insertions(+), 18 deletions(-)
--- a/include/linux/mm.h~mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow
+++ a/include/linux/mm.h
@@ -1300,6 +1300,27 @@ static inline bool page_maybe_dma_pinned
GUP_PIN_COUNTING_BIAS;
}
+static inline bool is_cow_mapping(vm_flags_t flags)
+{
+ return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
+}
+
+/*
+ * This should most likely only be called during fork() to see whether we
+ * should break the cow immediately for a page on the src mm.
+ */
+static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
+ struct page *page)
+{
+ if (!is_cow_mapping(vma->vm_flags))
+ return false;
+
+ if (!atomic_read(&vma->vm_mm->has_pinned))
+ return false;
+
+ return page_maybe_dma_pinned(page);
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
--- a/mm/huge_memory.c~mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow
+++ a/mm/huge_memory.c
@@ -1100,9 +1100,7 @@ int copy_huge_pmd(struct mm_struct *dst_
* best effort that the pinned pages won't be replaced by another
* random page during the coming copy-on-write.
*/
- if (unlikely(is_cow_mapping(vma->vm_flags) &&
- atomic_read(&src_mm->has_pinned) &&
- page_maybe_dma_pinned(src_page))) {
+ if (unlikely(page_needs_cow_for_dma(vma, src_page))) {
pte_free(dst_mm, pgtable);
spin_unlock(src_ptl);
spin_unlock(dst_ptl);
@@ -1214,9 +1212,7 @@ int copy_huge_pud(struct mm_struct *dst_
}
/* Please refer to comments in copy_huge_pmd() */
- if (unlikely(is_cow_mapping(vma->vm_flags) &&
- atomic_read(&src_mm->has_pinned) &&
- page_maybe_dma_pinned(pud_page(pud)))) {
+ if (unlikely(page_needs_cow_for_dma(vma, pud_page(pud)))) {
spin_unlock(src_ptl);
spin_unlock(dst_ptl);
__split_huge_pud(vma, src_pud, addr);
--- a/mm/internal.h~mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow
+++ a/mm/internal.h
@@ -296,11 +296,6 @@ static inline unsigned int buddy_order(s
*/
#define buddy_order_unsafe(page) READ_ONCE(page_private(page))
-static inline bool is_cow_mapping(vm_flags_t flags)
-{
- return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
-}
-
/*
* These three helpers classifies VMAs for virtual memory accounting.
*/
--- a/mm/memory.c~mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow
+++ a/mm/memory.c
@@ -809,12 +809,8 @@ copy_present_page(struct vm_area_struct
pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
struct page **prealloc, pte_t pte, struct page *page)
{
- struct mm_struct *src_mm = src_vma->vm_mm;
struct page *new_page;
- if (!is_cow_mapping(src_vma->vm_flags))
- return 1;
-
/*
* What we want to do is to check whether this page may
* have been pinned by the parent process. If so,
@@ -828,9 +824,7 @@ copy_present_page(struct vm_area_struct
* the page count. That might give false positives for
* for pinning, but it will work correctly.
*/
- if (likely(!atomic_read(&src_mm->has_pinned)))
- return 1;
- if (likely(!page_maybe_dma_pinned(page)))
+ if (likely(!page_needs_cow_for_dma(src_vma, page)))
return 1;
new_page = *prealloc;
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
hugetlb-pass-vma-into-huge_pte_alloc-and-huge_pmd_share.patch
hugetlb-pass-vma-into-huge_pte_alloc-and-huge_pmd_share-fix.patch
hugetlb-userfaultfd-forbid-huge-pmd-sharing-when-uffd-enabled.patch
mm-hugetlb-move-flush_hugetlb_tlb_range-into-hugetlbh.patch
hugetlb-userfaultfd-unshare-all-pmds-for-hugetlbfs-when-register-wp.patch
hugetlb-dedup-the-code-to-add-a-new-file_region.patch
hugetlg-break-earlier-in-add_reservation_in_range-when-we-can.patch
mm-introduce-page_needs_cow_for_dma-for-deciding-whether-cow.patch
mm-use-is_cow_mapping-across-tree-where-proper.patch
hugetlb-do-early-cow-when-page-pinned-on-src-mm.patch
