[RFC][PATCH 8/10] memcg: clean up charge/uncharge anon

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

This may need careful review.

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

In old codes, this function was used for other purposes rather
than charginc new anon pages. But now, this function is (ranamed) and
used only for new pages.

For the same kind of reason, ucharge_page() should use VM_BUG_ON().

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/memcontrol.c |   27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

Index: temp-mmotm/mm/memcontrol.c
===================================================================
--- temp-mmotm.orig/mm/memcontrol.c
+++ temp-mmotm/mm/memcontrol.c
@@ -1638,15 +1638,8 @@ int mem_cgroup_newpage_charge(struct pag
 		return 0;
 	if (PageCompound(page))
 		return 0;
-	/*
-	 * If already mapped, we don't have to account.
-	 * If page cache, page->mapping has address_space.
-	 * But page->mapping may have out-of-use anon_vma pointer,
-	 * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
-	 * is NULL.
-  	 */
-	if (page_mapped(page) || (page->mapping && !PageAnon(page)))
-		return 0;
+	/* This function is "newpage_charge" and called right after alloc */
+	VM_BUG_ON(page_mapped(page) || (page->mapping && !PageAnon(page)));
 	if (unlikely(!mm))
 		mm = &init_mm;
 	return mem_cgroup_charge_common(page, mm, gfp_mask,
@@ -1901,11 +1894,11 @@ unlock_out:
 
 void mem_cgroup_uncharge_page(struct page *page)
 {
-	/* early check. */
-	if (page_mapped(page))
-		return;
-	if (page->mapping && !PageAnon(page))
-		return;
+	/*
+ 	 * Called when anonymous page's page->mapcount goes down to zero,
+ 	 * or cancel a charge gotten by newpage_charge().
+	 */
+	VM_BUG_ON(page_mapped(page) || (page->mapping && !PageAnon(page)));
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 

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