linux-kernel - [PATCH -mm 09/12] fork: do not charge thread

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Message-ID: <14c6879ed1a974c3fe87d4b4d660bc0ac32f0a1f.1393423762.git.vdavydov@parallels.com>
Date:	Wed, 26 Feb 2014 19:05:14 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	<akpm@...ux-foundation.org>
CC:	<hannes@...xchg.org>, <mhocko@...e.cz>, <glommer@...il.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<devel@...nvz.org>, Frederic Weisbecker <fweisbec@...hat.com>
Subject: [PATCH -mm 09/12] fork: do not charge thread_info to kmemcg

This patch reverts 2ad306b17c0a ("fork: protect architectures where
THREAD_SIZE >= PAGE_SIZE against fork bombs").

The reasoning behind this is that charging thread_info is the last piece
that prevents us from reparenting kmemcg on css offline. The point is
that we can't reliably track all thread_info pages accounted to a
particular cgroup, because (a) it is freed in __put_task_struct and (b)
on exit tasks are moved to the root cgroup. That said, given a cgroup
there is no sane way to find all tasks (including zombies) that charged
thread_info to this cgroup. Of course, we could uncharge thread_info on
task exit, but that wouldn't help us against fork bombs. So revert and
forget about this.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Glauber Costa <glommer@...il.com>
Cc: Frederic Weisbecker <fweisbec@...hat.com>
---
 include/linux/thread_info.h |    2 --
 kernel/fork.c               |    4 ++--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index fddbe2023a5d..1807bb194816 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -61,8 +61,6 @@ extern long do_no_restart_syscall(struct restart_block *parm);
 # define THREADINFO_GFP		(GFP_KERNEL | __GFP_NOTRACK)
 #endif
 
-#define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
-
 /*
  * flag set/clear/test wrappers
  * - pass TIF_xxxx constants to these functions
diff --git a/kernel/fork.c b/kernel/fork.c
index b41022f5d307..2431645d4c91 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -148,7 +148,7 @@ void __weak arch_release_thread_info(struct thread_info *ti)
 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 						  int node)
 {
-	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
+	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
 					     THREAD_SIZE_ORDER);
 
 	return page ? page_address(page) : NULL;
@@ -156,7 +156,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 
 static inline void free_thread_info(struct thread_info *ti)
 {
-	free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
+	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 }
 # else
 static struct kmem_cache *thread_info_cache;
-- 
1.7.10.4

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