Re: [PATCH] mm: compaction: fix echo 1 > compact_memory return error issue

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Sun, Jan 06, 2013 at 08:11:58AM +0000, Liu Hui-R64343 wrote:
>>-----Original Message-----
>>From: Wanpeng Li [mailto:liwanp@linux.vnet.ibm.com]
>>Sent: Sunday, January 06, 2013 4:00 PM
>>To: Liu Hui-R64343
>>Cc: linux-kernel@vger.kernel.org; mgorman@suse.de; akpm@linux-
>>foundation.org; riel@redhat.com; minchan@kernel.org;
>>kamezawa.hiroyu@jp.fujitsu.com; linux-mm@kvack.org
>>Subject: Re: [PATCH] mm: compaction: fix echo 1 > compact_memory return
>>error issue
>>
>>On Sun, Jan 06, 2013 at 03:44:33PM +0800, Jason Liu wrote:
>>
>>Hi Jason,
>>
>>>when run the folloing command under shell, it will return error sh/$
>>>echo 1 > /proc/sys/vm/compact_memory sh/$ sh: write error: Bad address
>>>
>>
>>How can you modify the value through none privileged user since the mode
>>== 0200?
>
>I write it through privileged user(root). I'm using the GNOME_Mobile rootfs.
>
>>
>>>After strace, I found the following log:
>>>...
>>>write(1, "1\n", 2)               = 3
>>>write(1, "", 4294967295)         = -1 EFAULT (Bad address)
>>>write(2, "echo: write error: Bad address\n", 31echo: write error: Bad
>>>address
>>>) = 31
>>>
>>>This tells system return 3(COMPACT_COMPLETE) after write data to
>>compact_memory.
>>>
>>>The fix is to make the system just return 0 instead 3(COMPACT_COMPLETE)
>>>from sysctl_compaction_handler after compaction_nodes finished.
>>
>>What's the special scenario you are in? I couldn't figure out the similar error
>>against latest 3.8-rc2, how could you reproduce it?
>
>I'm using the BusyBox v1.20.2 () built-in shell (ash), it reproduces the issue: 100%.
>
>root@freescale /$ sh
>
>
>BusyBox v1.20.2 () built-in shell (ash)
>Enter 'help' for a list of built-in commands.
>
>Could you run strace and see the log:  strace echo 1 > /proc/sys/vm/compact_memory
>

I test it on my desktop against latest 3.8-rc2, can't repoduce it. :)

write(1, "1\n", 2)                      = 3
close(1)                                = 0
munmap(0xb779c000, 4096)                = 0
close(2)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

Regards,
Wanpeng Li 

>>
>>Regards,
>>Wanpeng Li
>>
>>>
>>>Suggested-by:David Rientjes <rientjes@google.com> Cc:Mel Gorman
>>><mgorman@suse.de> Cc:Andrew Morton <akpm@linux-foundation.org>
>>Cc:Rik
>>>van Riel <riel@redhat.com> Cc:Minchan Kim <minchan@kernel.org>
>>>Cc:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>>Signed-off-by: Jason Liu <r64343@freescale.com>
>>>---
>>> mm/compaction.c |    6 ++----
>>> 1 files changed, 2 insertions(+), 4 deletions(-)
>>>
>>>diff --git a/mm/compaction.c b/mm/compaction.c index 6b807e4..f8f5c11
>>>100644
>>>--- a/mm/compaction.c
>>>+++ b/mm/compaction.c
>>>@@ -1210,7 +1210,7 @@ static int compact_node(int nid)  }
>>>
>>> /* Compact all nodes in the system */
>>>-static int compact_nodes(void)
>>>+static void compact_nodes(void)
>>> {
>>> 	int nid;
>>>
>>>@@ -1219,8 +1219,6 @@ static int compact_nodes(void)
>>>
>>> 	for_each_online_node(nid)
>>> 		compact_node(nid);
>>>-
>>>-	return COMPACT_COMPLETE;
>>> }
>>>
>>> /* The written value is actually unused, all memory is compacted */ @@
>>>-1231,7 +1229,7 @@ int sysctl_compaction_handler(struct ctl_table *table,
>>int write,
>>> 			void __user *buffer, size_t *length, loff_t *ppos)  {
>>> 	if (write)
>>>-		return compact_nodes();
>>>+		compact_nodes();
>>>
>>> 	return 0;
>>> }
>>>--
>>>1.7.5.4
>>>
>>>
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>

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