Messages in this thread | | | Subject | Re: [PATCH] Revert "mm/page_alloc: protect pcp->batch accesses with ACCESS_ONCE" | From | Hekuang <> | Date | Thu, 31 Mar 2016 09:14:42 +0800 |
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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 :)
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