linux-kernel - Re: VM - a plenty of inactive memory

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Message-ID: <Pine.LNX.4.61.0804111024020.4784@chaos.analogic.com>
Date:	Fri, 11 Apr 2008 10:34:10 -0400
From:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
To:	"Andreas Grimm" <agrimm61@...il.com>
Cc:	"Johannes Weiner" <hannes@...urebad.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: VM - a plenty of inactive memory

On Fri, 11 Apr 2008, Andreas Grimm wrote:

> Hi everybody,
>
> i investigated this further. The tunables swappiness, drop_caches etc.
> are no options to solve this. The problem is becoming very unpleasent,
> because the system isn't able to cache that much:
>
> The 16GB system (expected behaviour):
> MemTotal:     16619808 kB
> MemFree:       4490032 kB
> Cached:        6929448 kB
> Inactive:      1670812 kB
>
> The 32GB system :
> MemTotal:     33265916 kB
> MemFree:        600000 kB
> Cached:        1561124 kB
> Inactive:     25873128 kB
>
> Don't you think this is insane? Wasting 25GB at the expense of caching
> (compare the cached value)? I'm clueless about this issue. Who (which
> process) owns that memory? Is there a way to flush this inactive
> memory? I assume that this memory hasn't been reclaimed for days,
> because the amount of inactive memory is at this level for days now.
>
> All values in /proc/sys/vm are at the defaults again, on both systems.
>
> Any help would be appreciated.
>
> Andreas

Wasting 25GB? It looks to me as though the kernel cached
(didn't write pages to disk yet) just about all it needed,
and there is lots of memory that it just doesn't need
  --yet! This means that if you have tasks that need memory
in a hurry, they'll get it without any disk accesses.

The kernel doesn't expand to use all the memory just to
spread itself all over the place. It uses what it needs,
caches some buffered data, and keepts track of all the
memory it has. If you want to use more cache, do '-lsR /'.
That'll read every directory into memory. It probably
won't go away until someody needs more memory.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.29 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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