[PATCH] memcg: remove charge variable in unmap_and_move

[Minchan Kim <minchan.kim@xxxxxxxxx>]

memcg charge/uncharge could be handled by mem_cgroup_[prepare/end]
migration itself so charge local variable in unmap_and_move lost the role
since we introduced 01b1ae63c2.

In addition, the variable name is not good like below.

int unmap_and_move()
{
	charge = mem_cgroup_prepare_migration(xxx);
	..
		BUG_ON(charge); <-- BUG if it is charged?
		..
		uncharge:
		if (!charge)    <-- why do we have to uncharge !charge?
			mem_group_end_migration(xxx);
	..
}

So let's remove unnecessary and confusing variable.

Suggested-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/migrate.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index b8a32da..e393841 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -623,7 +623,6 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 	struct page *newpage = get_new_page(page, private, &result);
 	int remap_swapcache = 1;
 	int rcu_locked = 0;
-	int charge = 0;
 	struct mem_cgroup *mem = NULL;
 	struct anon_vma *anon_vma = NULL;
 
@@ -662,12 +661,10 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 	}
 
 	/* charge against new page */
-	charge = mem_cgroup_prepare_migration(page, newpage, &mem);
-	if (charge == -ENOMEM) {
-		rc = -ENOMEM;
+	rc = mem_cgroup_prepare_migration(page, newpage, &mem);
+	if (rc == -ENOMEM)
 		goto unlock;
-	}
-	BUG_ON(charge);
+	BUG_ON(rc);
 
 	if (PageWriteback(page)) {
 		if (!force || !sync)
@@ -760,8 +757,7 @@ rcu_unlock:
 	if (rcu_locked)
 		rcu_read_unlock();
 uncharge:
-	if (!charge)
-		mem_cgroup_end_migration(mem, page, newpage, rc == 0);
+	mem_cgroup_end_migration(mem, page, newpage, rc == 0);
 unlock:
 	unlock_page(page);
 
-- 
1.7.0.4

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