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    SubjectRe: [PATCHv4 03/39] mm: implement zero_huge_user_segment and friends
    Date
    Hillf Danton wrote:
    > On Sun, May 12, 2013 at 9:23 AM, Kirill A. Shutemov
    > <kirill.shutemov@linux.intel.com> wrote:
    > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    > >
    > > Let's add helpers to clear huge page segment(s). They provide the same
    > > functionallity as zero_user_segment and zero_user, but for huge pages.
    > >
    > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > > ---
    > > include/linux/mm.h | 7 +++++++
    > > mm/memory.c | 36 ++++++++++++++++++++++++++++++++++++
    > > 2 files changed, 43 insertions(+)
    > >
    > > diff --git a/include/linux/mm.h b/include/linux/mm.h
    > > index c05d7cf..5e156fb 100644
    > > --- a/include/linux/mm.h
    > > +++ b/include/linux/mm.h
    > > @@ -1797,6 +1797,13 @@ extern void dump_page(struct page *page);
    > > extern void clear_huge_page(struct page *page,
    > > unsigned long addr,
    > > unsigned int pages_per_huge_page);
    > > +extern void zero_huge_user_segment(struct page *page,
    > > + unsigned start, unsigned end);
    > > +static inline void zero_huge_user(struct page *page,
    > > + unsigned start, unsigned len)
    > > +{
    > > + zero_huge_user_segment(page, start, start + len);
    > > +}
    > > extern void copy_user_huge_page(struct page *dst, struct page *src,
    > > unsigned long addr, struct vm_area_struct *vma,
    > > unsigned int pages_per_huge_page);
    > > diff --git a/mm/memory.c b/mm/memory.c
    > > index f7a1fba..f02a8be 100644
    > > --- a/mm/memory.c
    > > +++ b/mm/memory.c
    > > @@ -4266,6 +4266,42 @@ void clear_huge_page(struct page *page,
    > > }
    > > }
    > >
    > > +void zero_huge_user_segment(struct page *page, unsigned start, unsigned end)
    > > +{
    > > + int i;
    > > + unsigned start_idx, end_idx;
    > > + unsigned start_off, end_off;
    > > +
    > > + BUG_ON(end < start);
    > > +
    > > + might_sleep();
    > > +
    > > + if (start == end)
    > > + return;
    > > +
    > > + start_idx = start >> PAGE_SHIFT;
    > > + start_off = start & ~PAGE_MASK;
    > > + end_idx = (end - 1) >> PAGE_SHIFT;
    > > + end_off = ((end - 1) & ~PAGE_MASK) + 1;
    > > +
    > > + /*
    > > + * if start and end are on the same small page we can call
    > > + * zero_user_segment() once and save one kmap_atomic().
    > > + */
    > > + if (start_idx == end_idx)
    > > + return zero_user_segment(page + start_idx, start_off, end_off);
    > > +
    > > + /* zero the first (possibly partial) page */
    > > + zero_user_segment(page + start_idx, start_off, PAGE_SIZE);
    > > + for (i = start_idx + 1; i < end_idx; i++) {
    > > + cond_resched();
    > > + clear_highpage(page + i);
    > > + flush_dcache_page(page + i);
    >
    > Can we use the function again?
    > zero_user_segment(page + i, 0, PAGE_SIZE);

    No. zero_user_segment() is memset()-based. clear_highpage() is higly
    optimized for page clearing on many architectures.

    --
    Kirill A. Shutemov


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