On Tue, Apr 29, 2014 at 05:42:28PM +0800, Jianyu Zhan wrote:
> Currently, put_compound_page should carefully handle tricky case
> to avoid racing with compound page releasing or spliting, which
> makes it growing quite lenthy(about 200+ lines) and need deep
> tab indention, which makes it quite hard to follow and maintain.
>
> Now based on two helpers introduced in the previous patch
> ("mm/swap.c: introduce put_[un]refcounted_compound_page helpers
> for spliting put_compound_page"), this patch just replaces those
> two lenthy code path with these two helpers, respectively.
> Also, it has some comment rephrasing.
>
> After this patch, the put_compound_page() will be very compact,
> thus easy to read and maintain.
>
> After spliting, the object file is of same size as the original one.
> Actually, I've diff'ed put_compound_page()'s orginal disassemble code
> and the patched disassemble code, the are 100% the same!
>
> This fact shows that this spliting has no functinal change,
> but it brings readability.
>
> This patch and the previous one blow the code by 32 lines, which
> mostly credits to comments.
>
> Signed-off-by: Jianyu Zhan <nasa4836@xxxxxxxxx>
> ---
> mm/swap.c | 142 +++++++-------------------------------------------------------
> 1 file changed, 16 insertions(+), 126 deletions(-)
>
> diff --git a/mm/swap.c b/mm/swap.c
> index a576449..d8654d8 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -225,6 +225,11 @@ static void put_compound_page(struct page *page)
> {
> struct page *page_head;
>
> + /*
> + * We see the PageCompound set and PageTail not set, so @page maybe:
> + * 1. hugetlbfs head page, or
> + * 2. THP head page.
3. Head of slab compound page.
> + */
> if (likely(!PageTail(page))) {
> if (put_page_testzero(page)) {
> /*
> @@ -239,135 +244,20 @@ static void put_compound_page(struct page *page)
> return;
> }
>
...
> + * We see the PageCompound set and PageTail set, so @page maybe:
> + * 1. a tail hugetlbfs page, or
> + * 2. a tail THP page, or
> + * 3. a split THP page.
4. Tail of slab compound page
--
Kirill A. Shutemov
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