[PATCH] memcg: further checking of disabled flag

[Hugh Dickins <hugh@veritas.com>]

Further adjustments to the mem_cgroup_subsys.disabled tests: add one to
mem_cgroup_shrink_usage; move mem_cgroup_charge_common's into its callers,
before they've done any work; and add one to mem_cgroup_move_lists, to
avoid the overhead of its bit spin locking and unlocking.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
Should follow mmotm's memcg-clean-up-checking-of-the-disabled-flag.patch

 mm/memcontrol.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- mmotm/mm/memcontrol.c	2008-06-27 13:39:20.000000000 +0100
+++ linux/mm/memcontrol.c	2008-06-27 17:32:29.000000000 +0100
@@ -354,6 +354,9 @@ void mem_cgroup_move_lists(struct page *
 	struct mem_cgroup_per_zone *mz;
 	unsigned long flags;
 
+	if (mem_cgroup_subsys.disabled)
+		return;
+
 	/*
 	 * We cannot lock_page_cgroup while holding zone's lru_lock,
 	 * because other holders of lock_page_cgroup can be interrupted
@@ -533,9 +536,6 @@ static int mem_cgroup_charge_common(stru
 	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct mem_cgroup_per_zone *mz;
 
-	if (mem_cgroup_subsys.disabled)
-		return 0;
-
 	pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
 	if (unlikely(pc == NULL))
 		goto err;
@@ -620,6 +620,9 @@ err:
 
 int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
 {
+	if (mem_cgroup_subsys.disabled)
+		return 0;
+
 	/*
 	 * If already mapped, we don't have to account.
 	 * If page cache, page->mapping has address_space.
@@ -638,6 +641,9 @@ int mem_cgroup_charge(struct page *page,
 int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask)
 {
+	if (mem_cgroup_subsys.disabled)
+		return 0;
+
 	/*
 	 * Corner case handling. This is called from add_to_page_cache()
 	 * in usual. But some FS (shmem) precharges this page before calling it
@@ -789,6 +795,9 @@ int mem_cgroup_shrink_usage(struct mm_st
 	int progress = 0;
 	int retry = MEM_CGROUP_RECLAIM_RETRIES;
 
+	if (mem_cgroup_subsys.disabled)
+		return 0;
+
 	rcu_read_lock();
 	mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
 	css_get(&mem->css);