linux-kernel - Re: [PATCH] sysctl: vfs_cache

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Message-ID: <45FEF5BC.90809@oracle.com>
Date:	Mon, 19 Mar 2007 13:42:36 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"H. Peter Anvin" <hpa@...or.com>, "J.H." <warthog9@...nel.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sysctl: vfs_cache_divisor

Andrew Morton wrote:
> On Mon, 19 Mar 2007 12:27:40 -0700
> Randy Dunlap <randy.dunlap@...cle.com> wrote:
> 
>> +The default vfs_cache_divisor value is 100 (like percent).  However, for
>> +extremely large systems where a value of vfs_cache_pressure of less than
>> +1 percent is desirable, using a larger vfs_cache_divisor enables this wanted
>> +characteristic.
> 
> The one-percent-granularity problem also applies to /proc/sys/vm/*dirty*
> and possibly other things.  So any fix we do should be applicable to those
> as well.
> 
> And I'm not really sure how we should do this.  I do think that we should
> change the kernel so these knobs are internally higher-resolution.  So, for
> example, we switch all the logic so that instead of these variables
> representing 1/100th, they instead represent 1/1000000th, for example.
> 
> Then, we change the top-level /proc handler to do the 1/100th <-> 1/1000000th
> conversion.  So the rest of the kernel doesn't have to know about it.
> 
> The we duplicate all the relevant /proc knobs:
> 
> cat /proc/sys/vm/dirty_ratio
> 30
> cat /proc/sys/vm/hires-dirty_ratio/
> 300000
> 
> Or we do something else ;)

Sounds better.  I wasn't very keen on the userspace interface that this
exposed.  Will look at those.

-- 
~Randy
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