Hillf Danton wrote:
> On Sun, May 12, 2013 at 9:23 AM, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx>
> > ---
> > 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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