On Thu, 26 Apr 2012 15:57:30 -0700 (PDT)
David Rientjes <rientjes@xxxxxxxxxx> wrote:
> mm->page_table_lock is hotly contested for page fault tests and isn't
> necessary to do mem_cgroup_uncharge_page() in do_huge_pmd_wp_page().
>
> ...
>
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -968,8 +968,10 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> spin_lock(&mm->page_table_lock);
> put_page(page);
> if (unlikely(!pmd_same(*pmd, orig_pmd))) {
> + spin_unlock(&mm->page_table_lock);
> mem_cgroup_uncharge_page(new_page);
> put_page(new_page);
> + goto out;
> } else {
> pmd_t entry;
> VM_BUG_ON(!PageHead(page));
But this is on the basically-never-happens race path and will surely have no
measurable benefit?
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