linux-kernel - Re: [PATCHv4 19/24] thp, mm: use migration entries to freeze page counts on split

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Date:	Mon, 30 Mar 2015 19:49:43 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv4 19/24] thp, mm: use migration entries to freeze page counts on split

"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> writes:

> Currently, we rely on compound_lock() to get page counts stable on
> splitting page refcounting. To get it work we also take the lock on
> get_page() and put_page() which is hot path.
>
> This patch rework splitting code to setup migration entries to stabilaze
> page count/mapcount before distribute refcounts. It means we don't need
> to compound lock in get_page()/put_page().
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  include/linux/migrate.h |   3 +
>  include/linux/mm.h      |   1 +
>  include/linux/pagemap.h |   9 ++-
>  mm/huge_memory.c        | 188 +++++++++++++++++++++++++++++++++++-------------
>  mm/internal.h           |  26 +++++--
>  mm/migrate.c            |  79 +++++++++++---------
>  mm/rmap.c               |  21 ------
>  7 files changed, 218 insertions(+), 109 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 78baed5f2952..b9bc86c24829 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -43,6 +43,9 @@ extern int migrate_page_move_mapping(struct address_space *mapping,
>  		struct page *newpage, struct page *page,
>  		struct buffer_head *head, enum migrate_mode mode,
>  		int extra_count);
> +extern int __remove_migration_pte(struct page *new, struct vm_area_struct *vma,
> +		unsigned long addr, pte_t *ptep, struct page *old);
> +
>  #else
>
>  static inline void putback_movable_pages(struct list_head *l) {}
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 28aeae6e553b..43a9993f1333 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -981,6 +981,7 @@ extern struct address_space *page_mapping(struct page *page);
>  /* Neutral page->mapping pointer to address_space or anon_vma or other */
>  static inline void *page_rmapping(struct page *page)
>  {
> +	page = compound_head(page);
>  	return (void *)((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
>  }
>

The above hunk is related to this patch ?. Are we calling page_rmapping
on tail pages now ? If so it needs additonal comment why we handle them
differently now. Or split it to a seperate patch ?

-aneesh

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