linux-kernel - Re: [PATCH v4 1/2] mm: introduce page reference manipulation functions

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Date:	Wed, 2 Mar 2016 17:44:16 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 1/2] mm: introduce page reference manipulation
 functions

On 02/26/2016 01:58 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Success of CMA allocation largely depends on success of migration
> and key factor of it is page reference count. Until now, page reference
> is manipulated by direct calling atomic functions so we cannot follow up
> who and where manipulate it. Then, it is hard to find actual reason
> of CMA allocation failure. CMA allocation should be guaranteed to succeed
> so finding offending place is really important.
>
> In this patch, call sites where page reference is manipulated are converted
> to introduced wrapper function. This is preparation step to add tracepoint
> to each page reference manipulation function. With this facility, we can
> easily find reason of CMA allocation failure. There is no functional change
> in this patch.
>
> In addition, this patch also converts reference read sites. It will help
> a second step that renames page._count to something else and prevents later
> attempt to direct access to it (Suggested by Andrew).
>
> Acked-by: Michal Nazarewicz <mina86@...a86.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Even without Patch 2/2 this is a nice improvement.
Acked-by: Vlastimil Babka <vbabka@...e.cz>

Although somebody might be confused by page_ref_count() vs page_count(). 
Oh well.