Re: [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags

[Alex Shi]

在 2020/8/19 下午3:55, Anshuman Khandual 写道:
> 
> 
> On 08/19/2020 11:17 AM, Alex Shi wrote:
>> pageblock_flags is used as long, since every pageblock_flags is just 4
>> bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags,
>> that flag setting has to sync in cmpxchg with 7 or 15 other pageblock
>> flags. It would cause long waiting for sync.
>>
>> If we could change the pageblock_flags variable as char, we could use
>> char size cmpxchg, which just sync up with 2 pageblock flags. it could
>> relief much false sharing in cmpxchg.
> 
> Do you have numbers demonstrating claimed performance improvement
> after this change ?
> 

the performance data show in another email.

LKP reported the arm6 has a bug on this patchset, since it has no cmpxchgb
solution, so maybe let's fallback to cmpxchg on it.