linux-kernel - Re: Inactive memory keep growing and how to release it?

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Date:	Thu, 14 Mar 2013 11:14:03 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Lenky Gao <lenky.gao@...il.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Inactive memory keep growing and how to release it?

On Mon 04-03-13 17:52:22, Lenky Gao wrote:
> Hi,
> 
> When i just run a test on Centos 6.2 as follows:
> 
> #!/bin/bash
> 
> while true
> do
> 
> 	file="/tmp/filetest"
> 
> 	echo $file
> 
> 	dd if=/dev/zero of=${file} bs=512 count=204800 &> /dev/null
> 
> 	sleep 5
> done
> 
> the inactive memory keep growing:
> 
> #cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):   420144 kB
> ...
> #cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):   911912 kB
> ...
> #cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):  1547484 kB
> ...
> 
> and i cannot reclaim it:

How did you try to reclaim the memory? How much memory is still free?
Are you above watermaks (/proc/zoneinfo will tell you more)

> # cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):  1557684 kB
> # echo 3 > /proc/sys/vm/drop_caches
> # cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):  1520832 kB
> 
> I have tested on other version kernel, such as 2.6.30 and .6.11, the
> problom also exists.
> 
> When in the final situation, i cannot kmalloc a larger contiguous
> memory, especially in interrupt context.

This could be related to the memory fragmentation and your kernel seem
to be too large to have memory compaction which helps a lot in that
area.

> Can you give some tips to avoid this?

One way would be to increase /proc/sys/vm/min_free_kbytes which will
enlarge watermaks so the reclaim starts sooner.
 
> PS:
> # uname -a
> Linux localhost.localdomain 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6
> 19:48:22 GMT 2011 x86_64 x86_64 x86_64 GNU/Linux

This is really an old kernel and also a distribution one which might
contain a lot of patches on top of the core kernel. I would suggest to
contact Redhat or try to reproduce the issue with the vanilla and
up-to-date kernel and report here.
-- 
Michal Hocko
SUSE Labs
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