linux-kernel - Re: [PATCHv3 2/5] zsmalloc: use page->private instead of page->first

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Date:	Mon, 24 Aug 2015 17:04:43 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv3 2/5] zsmalloc: use page->private instead of
 page->first_page

On 08/19/2015 11:21 AM, Kirill A. Shutemov wrote:
> We are going to rework how compound_head() work. It will not use
> page->first_page as we have it now.
>
> The only other user of page->fisrt_page beyond compound pages is

                                ^ typo

> zsmalloc.
>
> Let's use page->private instead of page->first_page here. It occupies
> the same storage space.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/zsmalloc.c | 11 +++++------
>   1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0a7f81aa2249..a85754e69879 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -16,7 +16,7 @@
>    * struct page(s) to form a zspage.
>    *
>    * Usage of struct page fields:
> - *	page->first_page: points to the first component (0-order) page
> + *	page->private: points to the first component (0-order) page
>    *	page->index (union with page->freelist): offset of the first object
>    *		starting in this page. For the first page, this is
>    *		always 0, so we use this field (aka freelist) to point
> @@ -26,8 +26,7 @@
>    *
>    *	For _first_ page only:
>    *
> - *	page->private (union with page->first_page): refers to the
> - *		component page after the first page
> + *	page->private: refers to the component page after the first page
>    *		If the page is first_page for huge object, it stores handle.
>    *		Look at size_class->huge.
>    *	page->freelist: points to the first free object in zspage.
> @@ -770,7 +769,7 @@ static struct page *get_first_page(struct page *page)
>   	if (is_first_page(page))
>   		return page;
>   	else
> -		return page->first_page;
> +		return (struct page *)page_private(page);
>   }
>
>   static struct page *get_next_page(struct page *page)
> @@ -955,7 +954,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>   	 * Allocate individual pages and link them together as:
>   	 * 1. first page->private = first sub-page
>   	 * 2. all sub-pages are linked together using page->lru
> -	 * 3. each sub-page is linked to the first page using page->first_page
> +	 * 3. each sub-page is linked to the first page using page->private
>   	 *
>   	 * For each size class, First/Head pages are linked together using
>   	 * page->lru. Also, we set PG_private to identify the first page
> @@ -980,7 +979,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>   		if (i == 1)
>   			set_page_private(first_page, (unsigned long)page);
>   		if (i >= 1)
> -			page->first_page = first_page;
> +			set_page_private(first_page, (unsigned long)first_page);
>   		if (i >= 2)
>   			list_add(&page->lru, &prev_page->lru);
>   		if (i == class->pages_per_zspage - 1)	/* last page */
>

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