lkml.org 
[lkml]   [2016]   [Mar]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] Revert "mm/page_alloc: protect pcp->batch accesses with ACCESS_ONCE"
From
Date
Hi

在 2016/3/30 19:10, Michal Hocko 写道:
> On Wed 30-03-16 18:51:12, Hekuang wrote:
>> hi
>>
>> 在 2016/3/30 18:38, Mel Gorman 写道:
>>> On Wed, Mar 30, 2016 at 10:22:07AM +0000, He Kuang wrote:
>>>> This reverts commit 998d39cb236fe464af86a3492a24d2f67ee1efc2.
>>>>
>>>> When local irq is disabled, a percpu variable does not change, so we can
>>>> remove the access macros and let the compiler optimize the code safely.
>>>>
>>> batch can be changed from other contexts. Why is this safe?
>>>
>> I've mistakenly thought that per_cpu variable can only be accessed by that
>> cpu.
> git blame would point you to 998d39cb236f ("mm/page_alloc: protect
> pcp->batch accesses with ACCESS_ONCE"). I haven't looked into the code
> deeply to confirm this is still the case but it would be a good lead
> that this is not that simple. ACCESS_ONCE resp. {READ,WRITE}_ONCE are
> usually quite subtle so I would encourage you or anybody else who try to
> remove them to study the code and the history deeper before removing
> them.
>
Thank you for responding, I've read that commit and related articles and
not sending
mail casually, though you may think it's a stupid patch. I'm a beginner
and I think
sending mails to maillist is a effective way to learn kernel, And, sure
i'll be more careful and
well prepared next time :)

\
 
 \ /
  Last update: 2016-03-31 03:21    [W:0.075 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site