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Subject[PATCH 2/2] memcg: remove charge variable in unmap_and_move
Date
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@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
---
mm/memcontrol.c | 1 +
mm/migrate.c | 9 +++------
2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8ab8410..b1b572f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2804,6 +2804,7 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
/*
* Before starting migration, account PAGE_SIZE to mem_cgroup that the old
* page belongs to.
+ * Note : Should not return -EAGAIN. unmap_and_move depends on it.
*/
int mem_cgroup_prepare_migration(struct page *page,
struct page *newpage, struct mem_cgroup **ptr)
diff --git a/mm/migrate.c b/mm/migrate.c
index 8f0f131..5f2169f 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;

@@ -638,7 +637,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
if (unlikely(split_huge_page(page)))
goto move_newpage;

- /* prepare cgroup just returns 0 or -ENOMEM */
+ /* mem_cgroup_prepare_migration never returns -EAGAIN */
rc = -EAGAIN;

if (!trylock_page(page)) {
@@ -662,8 +661,7 @@ 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) {
+ if (mem_cgroup_prepare_migration(page, newpage, &mem)) {
rc = -ENOMEM;
goto unlock;
}
@@ -759,8 +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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