linux-kernel - Re: [PATCH 1/5] mm, page_owner: print migratetype of a page, not pageblock

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Date:	Thu, 5 Nov 2015 17:09:10 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Minchan Kim <minchan@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 1/5] mm, page_owner: print migratetype of a page, not
 pageblock

On Wed, Nov 04, 2015 at 04:00:57PM +0100, Vlastimil Babka wrote:
> The information in /sys/kernel/debug/page_owner includes the migratetype
> declared during the page allocation via gfp_flags. This is also checked against
> the pageblock's migratetype, and reported as Fallback allocation if these two
> differ (although in fact fallback allocation is not the only reason why they
> can differ).
> 
> However, the migratetype actually printed is the one of the pageblock, not of
> the page itself, so it's the same for all pages in the pageblock. This is
> apparently a bug, noticed when working on other page_owner improvements. Fixed.

We can guess page migratetype through gfp_mask output although it isn't
easy task for now. But, there is no way to know pageblock migratetype.
I used this to know how memory is fragmented.

Thanks.

> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/page_owner.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 983c3a1..a9f16b8 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -113,7 +113,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  			"PFN %lu Block %lu type %d %s Flags %s%s%s%s%s%s%s%s%s%s%s%s\n",
>  			pfn,
>  			pfn >> pageblock_order,
> -			pageblock_mt,
> +			page_mt,
>  			pageblock_mt != page_mt ? "Fallback" : "        ",
>  			PageLocked(page)	? "K" : " ",
>  			PageError(page)		? "E" : " ",
> -- 
> 2.6.2
> 
> --
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