linux-kernel - Re: [PATCH v2] Make VM_MAX_READAHEAD a kernel parameter

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Message-ID: <20100223022527.GB22370@discord.disaster>
Date:	Tue, 23 Feb 2010 13:25:27 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Nikanth Karthikesan <knikanth@...e.de>,
	Ankit Jain <radical@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] Make VM_MAX_READAHEAD a kernel parameter

On Sun, Feb 21, 2010 at 10:26:00PM +0800, Wu Fengguang wrote:
> Nikanth,
> 
> > > > +	readahead=	Default readahead value for block devices.
> > > > +
> > > 
> > > I think the description should define the units (kb) and valid value
> > > ranges e.g. page size to something not excessive - say 65536kb.  The
> > > above description is, IMO, useless without refering to the source to
> > > find out this information....
> > > 
> > 
> > The parameter can be specified with/without any suffix(k/m/g) that memparse() 
> > helper function can accept. So it can take 1M, 1024k, 1050620. I checked other 
> > parameters that use memparse() to get similar values and they didn't document 
> > it. May be this should be described here.
> 
> Hope this helps clarify things to user:
> 
> +       readahead=nn[KM]
> +                       Default max readahead size for block devices.
> +                       Range: 0; 4k - 128m

Yes, that is exactly what I was thinĸing of. Thanks.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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