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

[Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>]

On 02/26/2016 01:58 AM, js1304-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> From: Joonsoo Kim <iamjoonsoo.kim-Hm3cg6mZ9cc@public.gmane.org>
>
> 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-deATy8a+UHjQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim-Hm3cg6mZ9cc@public.gmane.org>

Even without Patch 2/2 this is a nice improvement.
Acked-by: Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>

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