Re: [PATCH v4] hugetlbfs: support split page table lock

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> writes:

> Hi,
>
> Kirill posted split_ptl patchset for thp today, so in this version
> I post only hugetlbfs part. I added Kconfig variables in following
> Kirill's patches (although without CONFIG_SPLIT_*_PTLOCK_CPUS.)
>
> This patch changes many lines, but all are in hugetlbfs specific code,
> so I think we can apply this independent of thp patches.
> -----
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Date: Fri, 13 Sep 2013 18:12:30 -0400
> Subject: [PATCH v4] hugetlbfs: support split page table lock
>
> Currently all of page table handling by hugetlbfs code are done under
> mm->page_table_lock. So when a process have many threads and they heavily
> access to the memory, lock contention happens and impacts the performance.
>
> This patch makes hugepage support split page table lock so that we use
> page->ptl of the leaf node of page table tree which is pte for normal pages
> but can be pmd and/or pud for hugepages of some architectures.
>
> ChangeLog v4:
>  - introduce arch dependent macro ARCH_ENABLE_SPLIT_HUGETLB_PTLOCK
>    (only defined for x86 for now)
>  - rename USE_SPLIT_PTLOCKS_HUGETLB to USE_SPLIT_HUGETLB_PTLOCKS

Can we have separate locking for THP and hugetlb ? Doesn't both require us to
use same locking when updating pmd ?


-aneesh

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