Re: [PATCH v3 1/2] THP: avoid lock when check whether THP is in deferred list

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Hi Andrew,

On 5/4/23 19:48, kirill@xxxxxxxxxxxxx wrote:
> On Sat, Apr 29, 2023 at 04:27:58PM +0800, Yin Fengwei wrote:
>> free_transhuge_page() acquires split queue lock then check
>> whether the THP was added to deferred list or not. It brings
>> high deferred queue lock contention.
>>
>> It's safe to check whether the THP is in deferred list or not
>> without holding the deferred queue lock in free_transhuge_page()
>> because when code hit free_transhuge_page(), there is no one
>> tries to add the folio to _deferred_list.
>>
>> Running page_fault1 of will-it-scale + order 2 folio for anonymous
>> mapping with 96 processes on an Ice Lake 48C/96T test box, we could
>> see the 61% split_queue_lock contention:
>> -   63.02%     0.01%  page_fault1_pro  [kernel.kallsyms]         [k] free_transhuge_page
>>    - 63.01% free_transhuge_page
>>       + 62.91% _raw_spin_lock_irqsave
>>
>> With this patch applied, the split_queue_lock contention is less
>> than 1%.
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
I didn't get the green light for patch2 (which was trying to reduce lru lock contention)
from Matthew. It may need more time to figure out how to reduce lru lock contention.

I am wondering whether this patch1 (without patch2) can be picked as
  - It has nothing to do with patch2
  - It could reduce the deferred queue lock contention.
  - It got acked-by from Kirill.

Let me know if you want me to resend this patch1. Thanks.


Regards
Yin, Fengwei

> 




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