Re: [PATCH 8/8] Add VM counters for transparent hugepages

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Tue, 2011-02-22 at 17:52 -0800, Andi Kleen wrote:
> @@ -2286,6 +2290,9 @@ void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd)
>  		spin_unlock(&mm->page_table_lock);
>  		return;
>  	}
> +
> +	count_vm_event(THP_SPLIT);
> +
>  	page = pmd_page(*pmd);
>  	VM_BUG_ON(!page_count(page));
>  	get_page(page);

Hey Andi,

Your split counter tracks the split_huge_page_pmd() calls, but misses
plain split_huge_page() calls.  Did you do this on purpose?  Could we
move the counter in to the low-level split function like below?

---

 linux-2.6.git-dave/mm/huge_memory.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN mm/huge_memory.c~move-THP_SPLIT mm/huge_memory.c
--- linux-2.6.git/mm/huge_memory.c~move-THP_SPLIT	2011-02-24 14:37:32.825288409 -0800
+++ linux-2.6.git-dave/mm/huge_memory.c	2011-02-24 14:39:01.767939971 -0800
@@ -1342,6 +1342,8 @@ static void __split_huge_page(struct pag
 	BUG_ON(!PageHead(page));
 	BUG_ON(PageTail(page));
 
+	count_vm_event(THP_SPLIT);
+
 	mapcount = 0;
 	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
 		struct vm_area_struct *vma = avc->vma;
@@ -2293,8 +2295,6 @@ void __split_huge_page_pmd(struct mm_str
 		return;
 	}
 
-	count_vm_event(THP_SPLIT);
-
 	page = pmd_page(*pmd);
 	VM_BUG_ON(!page_count(page));
 	get_page(page);

-- Dave