Subject: Re: [PATCH V1 00/11] powerpc/mm/book3s64: Support for split pmd ptlock

From: Balbir Singh <[email-masked]>
Date: Wed, 18 Apr 2018 08:43:07 +1000

On Mon, 16 Apr 2018 16:57:12 +0530
"Aneesh Kumar K.V" <[email-masked]> wrote:

> This patch series add split pmd pagetable lock for book3s64. nohash64 also should
> be able to switch to this. I need to workout the code dependency. This series
> also migh have broken the build on platforms otherthan book3s64. I am sending this early
> to get feedback on whether we should continue with the approach.
> 
> We switch the pmd allocator to use something similar to what we already use for
> level 4 pagetable allocation. We get an order 0 page and divide that to fragments
> and hand over fragments when we get request for a pmd pagetable. The pmd lock is
> now stashed in the struct page backing the allocated page.

That's only for the THP case right?

> 
> The series helps in reducing lock contention on mm->page_table_lock.
>

The numbers look good.