linux-ext4 - Re: Inactive memory keep growing and how to release it?

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Message-ID: <20130312083711.GA1943@gmail.com>
Date:	Tue, 12 Mar 2013 16:37:11 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Lenky Gao <lenky.gao@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Inactive memory keep growing and how to release it?

Hi Gao,

On Tue, Mar 12, 2013 at 02:58:24PM +0800, 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):   554662 kB
> ...
> #cat /proc/meminfo | grep Inactive\(fi
> Inactive(file):   882824 kB
> 
> and i cannot reclaim it:
> 
> # cat /proc/meminfo | grep Inactive\(file\);
> Inactive(file):   882824 kB
> # sync;
> # echo 3 > /proc/sys/vm/drop_caches
> # cat /proc/meminfo | grep Inactive\(file\);
> Inactive(file):   777664 kB
> 
> My file system type is ext3, mounted with the option data=journal and
> it is easy to reproduce. If the mount option is data=ordered,
> reproducing this problom need more time. Because of the problom, when
> in the final situation, i cannot kmalloc a larger contiguous memory,
> especially in interrupt context. I have tested on other version
> kernel, such as 2.6.30 and 3.6.11, the problom also exists.
> 
> Is this a bug?

I don't think it is a bug.  If I understand correctly, when you try to
reclaim memory (sync and drop caches), the test script is still running,
right?  If so, that means that some memory will be re-dirtied again.  So
the number of inactive pages could not reduce as you expected.

Regards,
                                                - Zheng
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