Re: [PATCH 1/2] mem_cgroup: optimize the atomic count of wb_completion

From: brookxu
Date: Fri Sep 24 2021 - 09:26:41 EST

Thanks for your time.

Michal Hocko wrote on 2021/9/24 17:34:
> On Fri 24-09-21 14:46:22, brookxu wrote:
>> From: Chunguang Xu <brookxu@xxxxxxxxxxx>
>> In order to track inflight foreign writeback, we init
>> wb_completion.cnt to 1. For normal writeback, this cause
>> wb_wait_for_completion() to perform meaningless atomic
>> operations. Since foreign writebacks rarely occur in most
>> scenarios, we can init wb_completion.cnt to 0 and set
>> frn.done.cnt to 1. In this way we can avoid unnecessary
>> atomic operations.
> Does this lead to any measurable differences?

I created multiple cgroups that performed IO on multiple disks,
then flushed the cache with sync command, and no measurable
differences have been observed so far.