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SubjectRe: [RFC 3/4] mm, page_alloc: move cpuset seqcount checking to slowpath
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On 01/18/2017 10:40 AM, Michal Hocko wrote:
> On Tue 17-01-17 23:16:09, Vlastimil Babka wrote:
>> This is a preparation for the following patch to make review simpler. While
>> the primary motivation is a bug fix, this could also save some cycles in the
>> fast path.
>
> I cannot say I would be happy about this patch :/ The code is still very
> confusing and subtle. I really think we should get rid of
> synchronization with the concurrent cpuset/mempolicy updates instead.
> Have you considered that instead?

Not so thoroughly yet, but I already suspect it would be intrusive for stable.
We could make copies of nodemask and mems_allowed and protect just the copying
with seqcount, but that would mean overhead and stack space. Also we might try
revert 682a3385e773 ("mm, page_alloc: inline the fast path of the zonelist
iterator") ...

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