linux-kernel - Re: [PATCH -mm] slub: document setting min order with debug_guardpage

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Message-ID: <alpine.DEB.2.00.1112131640240.32369@chino.kir.corp.google.com>
Date:	Tue, 13 Dec 2011 16:41:34 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Stanislaw Gruszka <sgruszka@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH -mm] slub: document setting min order with debug_guardpage_minorder
 > 0

On Tue, 13 Dec 2011, Rafael J. Wysocki wrote:

> > diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab
> > index 8b093f8..d84ca80 100644
> > --- a/Documentation/ABI/testing/sysfs-kernel-slab
> > +++ b/Documentation/ABI/testing/sysfs-kernel-slab
> > @@ -345,7 +345,9 @@ Description:
> >  		allocated.  It is writable and can be changed to increase the
> >  		number of objects per slab.  If a slab cannot be allocated
> >  		because of fragmentation, SLUB will retry with the minimum order
> > -		possible depending on its characteristics.
> > +		possible depending on its characteristics. 
> 
> Added trailing whitespace (please remove).
> 
> > +		When debug_guardpage_minorder > 0 parameter is specified, the
> > +		minimum possible order is used and cannot be changed.
> 
> Well, I'm not sure what you wanted to say, actually?  How does one change
> debug_guardpage_minorder (or specify it), for example?  Is it a kernel
> command-line switch?
> 

Yeah, we'll need a reference to Documentation/kernel-parameters.txt.

> Also I'm not sure what "cannot be changed" is supposed to mean.  Does it
> mean that /sys/cache/slab/cache/order has no effect in that case?
> 

Good point, we should say that "this tunable" cannot be used to change the 
order at runtime if debug_guardpage_minorder is used on the command line.

Stanislaw, one more revision?
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