Re: [PATCH] thp: reduce usage of huge zero page's atomic counter

[Andrew Morton]

On Tue, 30 Aug 2016 11:09:15 +0800 Aaron Lu <aaron.lu@xxxxxxxxx> wrote:

> >> Case used for test on Haswell EP:
> >> usemem -n 72 --readonly -j 0x200000 100G
> >> Which spawns 72 processes and each will mmap 100G anonymous space and
> >> then do read only access to that space sequentially with a step of 2MB.
> >>
> >> perf report for base commit:
> >>     54.03%  usemem   [kernel.kallsyms]   [k] get_huge_zero_page
> >> perf report for this commit:
> >>      0.11%  usemem   [kernel.kallsyms]   [k] mm_get_huge_zero_page
> > 
> > Does this mean that overall usemem runtime halved?
> 
> Sorry for the confusion, the above line is extracted from perf report.
> It shows the percent of CPU cycles executed in a specific function.
> 
> The above two perf lines are used to show get_huge_zero_page doesn't
> consume that much CPU cycles after applying the patch.
> 
> > 
> > Do we have any numbers for something which is more real-wordly?
> 
> Unfortunately, no real world numbers.
> 
> We think the global atomic counter could be an issue for performance
> so I'm trying to solve the problem.

So, umm, we don't actually know if the patch is useful to anyone?

Some more measurements would help things along, please.