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    SubjectRe: [PATCH v8 05/22] Add vm_replace_mixed()
    On Tue, Jul 22, 2014 at 03:47:53PM -0400, Matthew Wilcox wrote:
    > From: Matthew Wilcox <willy@linux.intel.com>
    >
    > vm_insert_mixed() will fail if there is already a valid PTE at that
    > location. The DAX code would rather replace the previous value with
    > the new PTE.
    >
    > Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
    > ---
    > include/linux/mm.h | 8 ++++++--
    > mm/memory.c | 34 +++++++++++++++++++++-------------
    > 2 files changed, 27 insertions(+), 15 deletions(-)
    >
    > diff --git a/include/linux/mm.h b/include/linux/mm.h
    > index e04f531..8d1194c 100644
    > --- a/include/linux/mm.h
    > +++ b/include/linux/mm.h
    > @@ -1958,8 +1958,12 @@ int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
    > int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
    > int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
    > unsigned long pfn);
    > -int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
    > - unsigned long pfn);
    > +int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
    > + unsigned long pfn, bool replace);
    > +#define vm_insert_mixed(vma, addr, pfn) \
    > + __vm_insert_mixed(vma, addr, pfn, false)
    > +#define vm_replace_mixed(vma, addr, pfn) \
    > + __vm_insert_mixed(vma, addr, pfn, true)
    > int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
    >
    >
    > diff --git a/mm/memory.c b/mm/memory.c
    > index 42bf429..cf06c97 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -1476,7 +1476,7 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
    > * pages reserved for the old functions anyway.
    > */
    > static int insert_page(struct vm_area_struct *vma, unsigned long addr,
    > - struct page *page, pgprot_t prot)
    > + struct page *page, pgprot_t prot, bool replace)
    > {
    > struct mm_struct *mm = vma->vm_mm;
    > int retval;
    > @@ -1492,8 +1492,12 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
    > if (!pte)
    > goto out;
    > retval = -EBUSY;
    > - if (!pte_none(*pte))
    > - goto out_unlock;
    > + if (!pte_none(*pte)) {
    > + if (!replace)
    > + goto out_unlock;
    > + VM_BUG_ON(!mutex_is_locked(&vma->vm_file->f_mapping->i_mmap_mutex));
    > + zap_page_range_single(vma, addr, PAGE_SIZE, NULL);

    zap_page_range_single() takes ptl by itself in zap_pte_range(). It's not
    going to work.

    And zap_page_range*() is pretty heavy weapon to shoot down one pte, which
    we already have pointer to. Why?

    --
    Kirill A. Shutemov


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