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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@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Gal Pressman <galpress@amazon.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Kirill Shutemov <kirill@shutemov.name>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Wei Zhang <wzam@amazon.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Xu 2021-03-12 21:07:26 -08:00 committed by Linus Torvalds
parent ca7e0457ef
commit 97a7e4733b
4 changed files with 24 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
include/linux/mm.h
View File

@ -1300,6 +1300,27 @@ static inline bool page_maybe_dma_pinned(struct page *page)
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

8
mm/huge_memory.c
View File

@ -1100,9 +1100,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* 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_mm, struct mm_struct *src_mm,
}
/* 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);

5
mm/internal.h
View File

@ -296,11 +296,6 @@ static inline unsigned int buddy_order(struct page *page)
*/
#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.
*/

8
mm/memory.c
View File

@ -809,12 +809,8 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
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 *dst_vma, struct vm_area_struct *src_vma
* 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;