linux-kernel - Re: [PATCH] mm/page_alloc: simplify kmem cgroup charge/uncharge code

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Date:   Tue, 8 Dec 2020 15:14:51 +0800
From:   Hui Su <sh_def@....com>
To:     linux-kernel@...r.kernel.org, sh_def@....com
Subject: Re: [PATCH] mm/page_alloc: simplify kmem cgroup charge/uncharge code

On Mon, Dec 07, 2020 at 09:28:46AM -0800, Shakeel Butt wrote:
> On Mon, Dec 7, 2020 at 6:22 AM Hui Su <sh_def@....com> wrote:
> 
> The reason to keep __memcg_kmem_[un]charge_page functions is that they
> were called in the very hot path. Can you please check the performance
> impact of your change and if the generated code is actually same or
> different.

Hi, Shakeel:

I objdump the mm/page_alloc.o and comapre them, it change the assemble code
indeed. In fact, it change some code order, which i personally think won't have
impact on performance. And i ran the ltp mm and conatiner test, it seems nothing
abnormal.

BUT i still want to check whether this change will have negative impact on
perforance due to this change code was called in the very hot path like you
said, AND saddly i did not find a way to quantify the impact on performance.
Can you give me some suggestion about how to quantify the performance or some
tool?

Thanks.