linux-kernel - Re: [PATCHv4 03/39] mm: implement zero_huge_user

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Date:	Thu, 23 May 2013 18:32:28 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Dave Hansen <dave@...1.net>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 03/39] mm: implement zero_huge_user_segment and friends

On Sun, May 12, 2013 at 9:23 AM, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.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@...ux.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);

> +       }
> +       /* zero the last (possibly partial) page */
> +       zero_user_segment(page + end_idx, 0, end_off);
> +}
> +
>  static void copy_user_gigantic_page(struct page *dst, struct page *src,
>                                     unsigned long addr,
>                                     struct vm_area_struct *vma,
> --
> 1.7.10.4
>
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