linux-kernel - [PATCH 1/2] fs: proc/stat: use num_online

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Date:	Wed, 28 May 2014 10:59:54 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Righi <andrea@...terlinux.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Thorsten Diehl <thorsten.diehl@...ibm.com>,
	Ian Kent <raven@...maw.net>,
	"Elliott, Robert (Server Storage)" <Elliott@...com>
Subject: [PATCH 1/2] fs: proc/stat: use num_online_cpus() for buffer size

The number of bytes contained 'within' /proc/stat depends on the number
of online cpus and not of the numbe of possible cpus.

This reduces the number of bytes requested for the initial buffer allocation
within stat_open(). Which is usually way too high and for nr_possible_cpus()
== 256 cpus would result in an order 4 allocation.

Order 4 allocations however may fail if memory is fragmented and we would
end up with an unreadable /proc/stat file:

62129.701569] sadc: page allocation failure: order:4, mode:0x1040d0
[62129.701573] CPU: 1 PID: 192063 Comm: sadc Not tainted 3.10.0-123.el7.s390x #1
[...]
[62129.701586] Call Trace:
[62129.701588] ([<0000000000111fbe>] show_trace+0xe6/0x130)
[62129.701591] [<0000000000112074>] show_stack+0x6c/0xe8
[62129.701593] [<000000000020d356>] warn_alloc_failed+0xd6/0x138
[62129.701596] [<00000000002114d2>] __alloc_pages_nodemask+0x9da/0xb68
[62129.701598] [<000000000021168e>] __get_free_pages+0x2e/0x58
[62129.701599] [<000000000025a05c>] kmalloc_order_trace+0x44/0xc0
[62129.701602] [<00000000002f3ffa>] stat_open+0x5a/0xd8
[62129.701604] [<00000000002e9aaa>] proc_reg_open+0x8a/0x140
[62129.701606] [<0000000000273b64>] do_dentry_open+0x1bc/0x2c8
[62129.701608] [<000000000027411e>] finish_open+0x46/0x60
[62129.701610] [<000000000028675a>] do_last+0x382/0x10d0
[62129.701612] [<0000000000287570>] path_openat+0xc8/0x4f8
[62129.701614] [<0000000000288bde>] do_filp_open+0x46/0xa8
[62129.701616] [<000000000027541c>] do_sys_open+0x114/0x1f0
[62129.701618] [<00000000005b1c1c>] sysc_tracego+0x14/0x1a

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 fs/proc/stat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 9d231e9e5f0e..3898ca5f1e92 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -184,7 +184,7 @@ static int show_stat(struct seq_file *p, void *v)
 
 static int stat_open(struct inode *inode, struct file *file)
 {
-	size_t size = 1024 + 128 * num_possible_cpus();
+	size_t size = 1024 + 128 * num_online_cpus();
 	char *buf;
 	struct seq_file *m;
 	int res;
-- 
1.8.5.5

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