On Thu, Dec 22, 2011 at 6:23 AM, Naoya Horiguchi
<n-horiguchi@xxxxxxxxxxxxx> wrote:
> Currently when we check if we can handle thp as it is or we need to
> split it into regular sized pages, we hold page table lock prior to
> check whether a given pmd is mapping thp or not. Because of this,
> when it's not "huge pmd" we suffer from unnecessary lock/unlock overhead.
> To remove it, this patch introduces a optimized check function and
> replace several similar logics with it.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> fs/proc/task_mmu.c | 74 ++++++++++------------------
> include/linux/huge_mm.h | 7 +++
> mm/huge_memory.c | 124 ++++++++++++++++++++++------------------------
> mm/mremap.c | 3 +-
> 4 files changed, 93 insertions(+), 115 deletions(-)
>
[...]
>
> +/*
> + * Returns 1 if a given pmd is mapping a thp and stable (not under splitting.)
> + * Returns 0 otherwise. Note that if it returns 1, this routine returns without
> + * unlocking page table locks. So callers must unlock them.
> + */
> +int check_and_wait_split_huge_pmd(pmd_t *pmd, struct vm_area_struct *vma)
> +{
> + if (!pmd_trans_huge(*pmd))
> + return 0;
> +
> + spin_lock(&vma->vm_mm->page_table_lock);
> + if (likely(pmd_trans_huge(*pmd))) {
> + if (pmd_trans_splitting(*pmd)) {
> + spin_unlock(&vma->vm_mm->page_table_lock);
> + wait_split_huge_page(vma->anon_vma, pmd);
return 0; yes?
> + } else {
> + /* Thp mapped by 'pmd' is stable, so we can
> + * handle it as it is. */
> + return 1;
> + }
> + }
> + spin_unlock(&vma->vm_mm->page_table_lock);
> + return 0;
> +}
> +
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