Re: [PATCH mm] introduce reverse buddy concept to reduce buddy fragment

From: Michal Hocko
Date: Tue Jul 04 2017 - 07:24:26 EST

On Tue 04-07-17 16:04:52, zhouxianrong wrote:
> every 2s i sample /proc/buddyinfo in the whole test process.
> the last about 90 samples were sampled after the test was done.

I've tried to explain to you that numbers without a proper testing
metodology and highlevel metrics you are interested in and comparision
to the base kernel are meaningless. I cannot draw any conclusion from
looking at numbers you have posted. Are high order allocations cheaper
to do with this patch? What about an averge order-0 allocation request?

You are touching memory allocator hot paths and those are really
sensitive to changes. It takes a lot of testing with different workloads
to prove that no new regressions are introduced. That being said, I
completely agree that reducing the memory fragmentation is an important
objective but touching the page allocator and adding new branches there
sounds like a problematic approach which would have to show _huge_
benefits to be mergeable. Is it possible to improve khugepaged to
accomplish the same thing?
Michal Hocko