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Subject[PATCH] memcg: clean up migration
Date
This patch cleans up unncessary BUG_ON check and confusing
charge variable.

That's because 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.

And mem_cgroup_prepare_migratio return 0 if only it is successful.
Otherwise, it jumps to unlock label to clean up so BUG_ON(charge)
isn;t meaningless.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
---
mm/memcontrol.c | 1 +
mm/migrate.c | 14 ++++----------
2 files changed, 5 insertions(+), 10 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2fc97fc..6832926 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2872,6 +2872,7 @@ 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.
+ * Return 0 if charge is successful. Otherwise return -errno.
*/
int mem_cgroup_prepare_migration(struct page *page,
struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
diff --git a/mm/migrate.c b/mm/migrate.c
index eb083a6..737c2e5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -622,7 +622,6 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
int *result = NULL;
struct page *newpage = get_new_page(page, private, &result);
int remap_swapcache = 1;
- int charge = 0;
struct mem_cgroup *mem;
struct anon_vma *anon_vma = NULL;

@@ -637,9 +636,7 @@ 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 */
rc = -EAGAIN;
-
if (!trylock_page(page)) {
if (!force)
goto move_newpage;
@@ -678,13 +675,11 @@ 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, GFP_KERNEL);
- if (charge == -ENOMEM) {
- rc = -ENOMEM;
+ rc = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
+ if (rc)
goto unlock;
- }
- BUG_ON(charge);

+ rc = -EAGAIN;
if (PageWriteback(page)) {
if (!force || !sync)
goto uncharge;
@@ -767,8 +762,7 @@ skip_unmap:
drop_anon_vma(anon_vma);

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);

--
1.7.1


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