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

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Message-ID: <4FE2D747.20506@jp.fujitsu.com>
Date:	Thu, 21 Jun 2012 17:11:51 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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

(2012/06/20 8:58), Andrew Morton wrote:
> On Mon, 18 Jun 2012 20:59:44 +0900
> Kamezawa Hiroyuki<kamezawa.hiroyu@...fujitsu.com>  wrote:
>
>>
>> By commit "memcg: move charges to root cgroup if use_hierarchy=0"
>> mem_cgroup_move_parent() only returns -EBUSY, -EINVAL.
>> So, we can remove -ENOMEM and -EINTR checks.
>>
>> Signed-off-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>> ---
>>   mm/memcontrol.c |    5 -----
>>   1 files changed, 0 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index cf8a0f6..726b7c6 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -3847,8 +3847,6 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
>>   		pc = lookup_page_cgroup(page);
>>
>>   		ret = mem_cgroup_move_parent(page, pc, memcg, GFP_KERNEL);
>> -		if (ret == -ENOMEM || ret == -EINTR)
>> -			break;
>>
>>   		if (ret == -EBUSY || ret == -EINVAL) {
>
> This looks a bit fragile - if mem_cgroup_move_parent() is later changed
> (intentionally or otherwise!) to return -Esomethingelse then
> mem_cgroup_force_empty_list() will subtly break.  Why not just do
>
> 		if (ret<  0)
>

You're right. I'm sorry I haven't done enough clean-ups.
I made 2 more patches...I'll repost/remake all paches if it's better.
one more patch will follow this email.
==
 From eee5f31fc6378da19705de7187bb3f219ef6d7f6 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Date: Thu, 21 Jun 2012 17:25:04 +0900
Subject: [PATCH 1/2] mem_cgroup_move_parent() doesn't need gfp_mask.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
  mm/memcontrol.c |    5 ++---
  1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 76d83a5..90a2ad4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2662,8 +2662,7 @@ out:
  
  static int mem_cgroup_move_parent(struct page *page,
  				  struct page_cgroup *pc,
-				  struct mem_cgroup *child,
-				  gfp_t gfp_mask)
+				  struct mem_cgroup *child)
  {
  	struct mem_cgroup *parent;
  	unsigned int nr_pages;
@@ -3837,7 +3836,7 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
  
  		pc = lookup_page_cgroup(page);
  
-		ret = mem_cgroup_move_parent(page, pc, memcg, GFP_KERNEL);
+		ret = mem_cgroup_move_parent(page, pc, memcg);
  
  		if (ret == -EBUSY || ret == -EINVAL) {
  			/* found lock contention or "pc" is obsolete. */
-- 
1.7.4.1











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