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

[Joonsoo Kim]

2016-03-03 1:44 GMT+09:00 Vlastimil Babka <vbabka@xxxxxxx>:
> On 02/26/2016 01:58 AM, js1304@xxxxxxxxx wrote:
>>
>> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>
>
> Even without Patch 2/2 this is a nice improvement.
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> Although somebody might be confused by page_ref_count() vs page_count(). Oh
> well.

Yes... it was pointed by Kirill before but consistency is not the purpose of
this patchset so I skipped it. There are too many sites (roughly 100) so I'm not
sure this code churn is worth doing now. If someone think it is really
important,
I will handle it after rc2.

Thanks.