linux-kernel - Re: [PATCH v3 3/3] slub: min order when debug_guardpage

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Date:	Thu, 8 Dec 2011 13:06:03 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
cc:	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>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH v3 3/3] slub: min order when debug_guardpage_minorder >
 0

On Thu, 8 Dec 2011, Stanislaw Gruszka wrote:

> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 7d2a996..a66be56 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -3645,6 +3645,9 @@ void __init kmem_cache_init(void)
> > >  	struct kmem_cache *temp_kmem_cache_node;
> > >  	unsigned long kmalloc_size;
> > >  
> > > +	if (debug_guardpage_minorder())
> > > +		slub_max_order = 0;
> > > +
> > >  	kmem_size = offsetof(struct kmem_cache, node) +
> > >  				nr_node_ids * sizeof(struct kmem_cache_node *);
> > > 
> > 
> > I'd recommend at least printing a warning about why slub_max_order was 
> > reduced because users may be concerned why they can't now change any 
> > cache's order with /sys/kernel/slab/cache/order.
> 
> It's only happen with debug_guardpage_minorder=N parameter, so
> perhaps I'll just document that in kernel-parameters.txt
> 

SLUB will output a line in the dmesg that specifies the possible orders so 
it would be helpful to also note that those can change because of 
debug_guardpage_minorder in both Documentation/vm/slub.txt and the "order" 
file entry in Documentation/ABI/testing/sysfs-kernel-slab.

Thanks!
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