Re: [PATCH 5/6] memcg: make mem_cgroup_reparent_charges non failing

Michal Hocko
2012-10-19T13:49:38Z

This is an updated version of the patch. I have dropped
.__DEPRECATED_clear_css_refs in this one as it makes the best sense to
me. I didn't add Tejun's Reviewed-by because of this change. Could you
recheck, please?
---
>From 6c1f2e76e254e7638ad8cc87f319e3492ac80c5b Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Wed, 17 Oct 2012 14:15:09 +0200
Subject: [PATCH] memcg: make mem_cgroup_reparent_charges non failing

Now that pre_destroy callbacks are called from within cgroup_lock and
the cgroup has been checked to be empty without any children then there
is no other way to fail.
mem_cgroup_pre_destroy doesn't have to take a reference to memcg's css
because all css' are marked dead already.

mem_cgroup_subsys.__DEPRECATED_clear_css_refs can be dropped as
mem_cgroup_pre_destroy cannot fail now.

Changes since v1
- drop __DEPRECATED_clear_css_refs

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
mm/memcontrol.c | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f57ba4c..b4d854e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3738,14 +3738,12 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
*
* Caller is responsible for holding css reference on the memcg.
*/
-static int mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
+static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
{
struct cgroup *cgrp = memcg->css.cgroup;
int node, zid;

do {
- if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
- return -EBUSY;
/* This is for making all *used* pages to be on LRU. */
lru_add_drain_all();
drain_all_stock_sync(memcg);
@@ -3771,8 +3769,6 @@ static int mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
* charge before adding to the LRU.
*/
} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0);
-
- return 0;
}

/*
@@ -3809,7 +3805,9 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg)

}
lru_add_drain();
- return mem_cgroup_reparent_charges(memcg);
+ mem_cgroup_reparent_charges(memcg);
+
+ return 0;
}

static int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
@@ -5013,13 +5011,9 @@ free_out:
static int mem_cgroup_pre_destroy(struct cgroup *cont)
{
struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
- int ret;

- css_get(&memcg->css);
- ret = mem_cgroup_reparent_charges(memcg);
- css_put(&memcg->css);
-
- return ret;
+ mem_cgroup_reparent_charges(memcg);
+ return 0;
}

static void mem_cgroup_destroy(struct cgroup *cont)
@@ -5621,7 +5615,6 @@ struct cgroup_subsys mem_cgroup_subsys = {
.base_cftypes = mem_cgroup_files,
.early_init = 0,
.use_id = 1,
- .__DEPRECATED_clear_css_refs = true,
};

#ifdef CONFIG_MEMCG_SWAP
--
1.7.10.4

--
Michal Hocko
SUSE Labs