linux-kernel - Re: [RFC] Limit the size of the pagecache

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Date:	Fri, 26 Jan 2007 02:29:55 -0800
From:	Andrew Morton <akpm@...l.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Christoph Lameter <clameter@....com>, aubreylee@...il.com,
	svaidy@...ux.vnet.ibm.com, nickpiggin@...oo.com.au,
	rgetz@...ckfin.uclinux.org, Michael.Hennerich@...log.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] Limit the size of the pagecache

On Wed, 24 Jan 2007 14:15:10 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> - One for stability
>   When a customer constructs their detabase(Oracle), the system often goes to oom.
>   This is because that the system cannot allocate DMA_ZOME memory for 32bit device.
>   (USB or e100)
>   Not allowing to use almost all pages as page cache (for temporal use) will be some help.
>   (Note: construction DB on ext3....so all writes are serialized and the system couldn't
>    free page cache.)

I'm surprised that any reasonable driver has a dependency on ZONE_DMA.  Are
you sure?  Send full oom-killer output, please.


> - One for tuing.
>   Sometimes our cutomer requests us to limit size of page-cache.
>   
>   Many cutomers's memory usage reaches 99.x%. (this is very common situation.)
>   If almost all memories are used by page-cache, and we can think we can free it.
>   But the customer cannot estimate what amount of page-cache can be freed (without 
>   perfromance regression).
>   
>   When a cutomer wants to add a new application, he tunes the system.
>   But memory usage is always 99%.
>   page-cache limitation is useful when the customer tunes his system and find
>   sets of data and page-cache. 
>   (Of course, we can use some other complicated resource management system for this.)
>   This will allow the users to decide that they need extra memory or not.
> 
>   And...some customers want to keep memory Free as much as possible.
>   99% memory usage makes insecure them ;)

Tell them to do "echo 3 > /proc/sys/vm/drop_caches", then wait three minutes?
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