[PATCH 3/6] memcg: avoid accounting special pages

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

There are not-on-LRU pages which can be mapped and they are not worth to
be accounted. (becasue we can't shrink them and need dirty codes to handle
specical case) We'd like to make use of usual objrmap/radix-tree's protcol
and don't want to account out-of-vm's control pages.

When special_mapping_fault() is called, page->mapping is tend to be NULL 
and it's charged as Anonymous page.
insert_page() also handles some special pages from drivers.

This patch is for avoiding to account special pages.

Changelog: v6 -> v7
  - style fix.
Changelog: v5 -> v6
  - modified Documentation.
  - fixed to charge only when a page is newly allocated.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

 Documentation/controllers/memory.txt |   24 ++++++++++++++++--------
 mm/memory.c                          |   25 +++++++++++--------------
 mm/rmap.c                            |    4 ++--
 3 files changed, 29 insertions(+), 24 deletions(-)

Index: mmotm-2.6.27-rc7+/mm/memory.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/memory.c
+++ mmotm-2.6.27-rc7+/mm/memory.c
@@ -1323,18 +1323,14 @@ static int insert_page(struct vm_area_st
 	pte_t *pte;
 	spinlock_t *ptl;
 
-	retval = mem_cgroup_charge(page, mm, GFP_KERNEL);
-	if (retval)
-		goto out;
-
 	retval = -EINVAL;
 	if (PageAnon(page))
-		goto out_uncharge;
+		goto out;
 	retval = -ENOMEM;
 	flush_dcache_page(page);
 	pte = get_locked_pte(mm, addr, &ptl);
 	if (!pte)
-		goto out_uncharge;
+		goto out;
 	retval = -EBUSY;
 	if (!pte_none(*pte))
 		goto out_unlock;
@@ -1350,8 +1346,6 @@ static int insert_page(struct vm_area_st
 	return retval;
 out_unlock:
 	pte_unmap_unlock(pte, ptl);
-out_uncharge:
-	mem_cgroup_uncharge_page(page);
 out:
 	return retval;
 }
@@ -2463,6 +2457,7 @@ static int __do_fault(struct mm_struct *
 	struct page *page;
 	pte_t entry;
 	int anon = 0;
+	int charged = 0;
 	struct page *dirty_page = NULL;
 	struct vm_fault vmf;
 	int ret;
@@ -2503,6 +2498,12 @@ static int __do_fault(struct mm_struct *
 				ret = VM_FAULT_OOM;
 				goto out;
 			}
+			if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
+				ret = VM_FAULT_OOM;
+				page_cache_release(page);
+				goto out;
+			}
+			charged = 1;
 			/*
 			 * Don't let another task, with possibly unlocked vma,
 			 * keep the mlocked page.
@@ -2543,11 +2544,6 @@ static int __do_fault(struct mm_struct *
 
 	}
 
-	if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
-		ret = VM_FAULT_OOM;
-		goto out;
-	}
-
 	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
 
 	/*
@@ -2585,7 +2581,8 @@ static int __do_fault(struct mm_struct *
 		/* no need to invalidate: a not-present page won't be cached */
 		update_mmu_cache(vma, address, entry);
 	} else {
-		mem_cgroup_uncharge_page(page);
+		if (charged)
+			mem_cgroup_uncharge_page(page);
 		if (anon)
 			page_cache_release(page);
 		else
Index: mmotm-2.6.27-rc7+/mm/rmap.c
===================================================================
--- mmotm-2.6.27-rc7+.orig/mm/rmap.c
+++ mmotm-2.6.27-rc7+/mm/rmap.c
@@ -725,8 +725,8 @@ void page_remove_rmap(struct page *page,
 			page_clear_dirty(page);
 			set_page_dirty(page);
 		}
-
-		mem_cgroup_uncharge_page(page);
+		if (PageAnon(page))
+			mem_cgroup_uncharge_page(page);
 		__dec_zone_page_state(page,
 			PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
 		/*
Index: mmotm-2.6.27-rc7+/Documentation/controllers/memory.txt
===================================================================
--- mmotm-2.6.27-rc7+.orig/Documentation/controllers/memory.txt
+++ mmotm-2.6.27-rc7+/Documentation/controllers/memory.txt
@@ -112,14 +112,22 @@ the per cgroup LRU.
 
 2.2.1 Accounting details
 
-All mapped pages (RSS) and unmapped user pages (Page Cache) are accounted.
-RSS pages are accounted at the time of page_add_*_rmap() unless they've already
-been accounted for earlier. A file page will be accounted for as Page Cache;
-it's mapped into the page tables of a process, duplicate accounting is carefully
-avoided. Page Cache pages are accounted at the time of add_to_page_cache().
-The corresponding routines that remove a page from the page tables or removes
-a page from Page Cache is used to decrement the accounting counters of the
-cgroup.
+All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
+(some pages which never be reclaimable and will not be on global LRU
+ are not accounted. we just accounts pages under usual vm management.)
+
+RSS pages are accounted at page_fault unless they've already been accounted
+for earlier. A file page will be accounted for as Page Cache when it's
+inserted into inode (radix-tree). While it's mapped into the page tables of
+processes, duplicate accounting is carefully avoided.
+
+A RSS page is unaccounted when it's fully unmapped. A PageCache page is
+unaccounted when it's removed from radix-tree.
+
+At page migration, accounting information is kept.
+
+Note: we just account pages-on-lru because our purpose is to control amount
+of used pages. not-on-lru pages are tend to be out-of-control from vm view.
 
 2.3 Shared Page Accounting
 

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