(2012/03/23 6:36), Andrew Morton wrote:

On Wed, 21 Mar 2012 18:52:04 +0900
KAMEZAWA Hiroyuki [off-list ref] wrote:

quoted

 static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
 			unsigned long addr, pte_t ptent, swp_entry_t *entry)
 {
-	int usage_count;
 	struct page *page = NULL;
 	swp_entry_t ent = pte_to_swp_entry(ptent);
 
 	if (!move_anon() || non_swap_entry(ent))
 		return NULL;
-	usage_count = mem_cgroup_count_swap_user(ent, &page);
-	if (usage_count > 1) { /* we don't move shared anon */
-		if (page)
-			put_page(page);
-		return NULL;
-	}
+#ifdef CONFIG_SWAP
+	/*
+	 * Avoid lookup_swap_cache() not to update statistics.
+	 */

I don't understand this comment - what is it trying to tell us?

High Dickins advised me to use find_get_page() rather than lookup_swap_cache()
because lookup_swap_cache() has some statistics with swap.

quoted

+	page = find_get_page(&swapper_space, ent.val);

The code won't even compile if CONFIG_SWAP=n?

mm/built-in.o: In function `mc_handle_swap_pte':
/home/kamezawa/Kernel/next/linux/mm/memcontrol.c:5172: undefined reference to `swapper_space'
make: *** [.tmp_vmlinux1] Error 1

Ah...but I think this function (mc_handle_swap_pte) itself should be under CONFIG_SWAP.
I'll post v2.

Thank you for review!
-Kame

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