Hi Naoya
On Sat, Jan 28, 2012 at 7:02 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>
>
> Changes since v3:
> - Fix likely/unlikely pattern in pmd_trans_huge_stable()
> - Change suffix from _stable to _lock
> - Introduce __pmd_trans_huge_lock() to avoid micro-regression
> - Return 1 when wait_split_huge_page path is taken
>
> Changes since v2:
> - Fix missing "return 0" in "thp under splitting" path
> - Remove unneeded comment
> - Change the name of check function to describe what it does
> - Add VM_BUG_ON(mmap_sem)
> ---
> fs/proc/task_mmu.c | 70 +++++++++------------------
> include/linux/huge_mm.h | 17 +++++++
> mm/huge_memory.c | 120 ++++++++++++++++++++++-------------------------
> 3 files changed, 96 insertions(+), 111 deletions(-)
>
[...]
> @@ -1064,21 +1056,14 @@ int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> {
> int ret = 0;
>
> - spin_lock(&vma->vm_mm->page_table_lock);
> - if (likely(pmd_trans_huge(*pmd))) {
> - ret = !pmd_trans_splitting(*pmd);
Here the value of ret is either false or true,
> - spin_unlock(&vma->vm_mm->page_table_lock);
> - if (unlikely(!ret))
> - wait_split_huge_page(vma->anon_vma, pmd);
> - else {
> - /*
> - * All logical pages in the range are present
> - * if backed by a huge page.
> - */
> - memset(vec, 1, (end - addr) >> PAGE_SHIFT);
> - }
> - } else
> + if (__pmd_trans_huge_lock(pmd, vma) == 1) {
> + /*
> + * All logical pages in the range are present
> + * if backed by a huge page.
> + */
> spin_unlock(&vma->vm_mm->page_table_lock);
> + memset(vec, 1, (end - addr) >> PAGE_SHIFT);
> + }
>
> return ret;
what is the returned value of this function? /Hillf
> }
> @@ -1108,20 +1093,10 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> goto out;
> }
--
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