linux-kernel - Re: [PATCH 2/2] memcg: clean up force_empty

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Date:	Thu, 21 Jun 2012 13:13:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/2] memcg: clean up force_empty_list() return value
 check

On Thu, 21 Jun 2012 17:17:01 +0900
Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> Now, mem_cgroup_force_empty_list() just returns 0 or -EBUSY and
> -EBUSY is just indicating 'you need to retry.'.
> This patch makes mem_cgroup_force_empty_list() as boolean function and
> make the logic simpler.
> 

For some reason I'm having trouble applying these patches - many
rejects, need to massage it in by hand.

> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3797,7 +3797,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>    * This routine traverse page_cgroup in given list and drop them all.
>    * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
>    */
> -static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
> +static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
>   				int node, int zid, enum lru_list lru)

Let's document the return value.  The mem_cgroup_force_empty_list()
comment is a mess so I tried to help it a bit.  How does this look?

--- a/mm/memcontrol.c~memcg-make-mem_cgroup_force_empty_list-return-bool-fix
+++ a/mm/memcontrol.c
@@ -3609,8 +3609,10 @@ unsigned long mem_cgroup_soft_limit_recl
 }
 
 /*
- * This routine traverse page_cgroup in given list and drop them all.
- * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
+ * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
+ * reclaim the pages page themselves - it just removes the page_cgroups.
+ * Returns true if some page_cgroups were not freed, indicating that the caller
+ * must retry this operation.
  */
 static bool mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
 				int node, int zid, enum lru_list lru)
_


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