Re: [PATCH 1/2] 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:

> 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 v2:
>  - add split ptl on other archs missed in v1
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
>  arch/powerpc/mm/hugetlbpage.c |  6 ++-
>  arch/tile/mm/hugetlbpage.c    |  6 ++-
>  include/linux/hugetlb.h       | 20 ++++++++++
>  mm/hugetlb.c                  | 92 ++++++++++++++++++++++++++-----------------
>  mm/mempolicy.c                |  5 ++-
>  mm/migrate.c                  |  4 +-
>  mm/rmap.c                     |  2 +-
>  7 files changed, 90 insertions(+), 45 deletions(-)
>
> diff --git v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c v3.11-rc3/arch/powerpc/mm/hugetlbpage.c
> index d67db4b..7e56cb7 100644
> --- v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/powerpc/mm/hugetlbpage.c
> @@ -124,6 +124,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  {
>  	struct kmem_cache *cachep;
>  	pte_t *new;
> +	spinlock_t *ptl;
>
>  #ifdef CONFIG_PPC_FSL_BOOK3E
>  	int i;
> @@ -141,7 +142,8 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  	if (! new)
>  		return -ENOMEM;
>
> -	spin_lock(&mm->page_table_lock);
> +	ptl = huge_pte_lockptr(mm, new);
> +	spin_lock(ptl);


Are you sure we can do that for ppc ?
	new = kmem_cache_zalloc(cachep, GFP_KERNEL|__GFP_REPEAT);

The page for new(pte_t) could be shared right ? which mean a deadlock ?

May be you should do it at the pmd level itself for ppc

>  #ifdef CONFIG_PPC_FSL_BOOK3E
>  	/*
>  	 * We have multiple higher-level entries that point to the same
> @@ -174,7 +176,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  #endif
>  	}
>  #endif
> -	spin_unlock(&mm->page_table_lock);
> +	spin_unlock(ptl);
>  	return 0;
>  }
>


-aneesh

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