linux-kernel - Re: [patch 1/2] slub: move min_partial to struct kmem

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Message-ID: <alpine.DEB.2.00.0902230821510.23216@chino.kir.corp.google.com>
Date:	Mon, 23 Feb 2009 08:23:26 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] slub: move min_partial to struct kmem_cache

On Mon, 23 Feb 2009, Christoph Lameter wrote:

> On Sun, 22 Feb 2009, David Rientjes wrote:
> 
> > +static void calculate_min_partial(struct kmem_cache *s, unsigned long min)
> > +{
> > +	if (min < MIN_PARTIAL)
> > +		min = MIN_PARTIAL;
> > +	else if (min > MAX_PARTIAL)
> > +		min = MAX_PARTIAL;
> > +	s->min_partial = min;
> > +}
> > +
> >  /*
> >   * calculate_sizes() determines the order and the distribution of data within
> >   * a slab object.
> > @@ -2319,6 +2317,11 @@ static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
> >  	if (!calculate_sizes(s, -1))
> >  		goto error;
> >
> > +	/*
> > +	 * The larger the object size is, the more pages we want on the partial
> > +	 * list to avoid pounding the page allocator excessively.
> > +	 */
> > +	calculate_min_partial(s, ilog2(s->size));
> >  	s->refcount = 1;
> >  #ifdef CONFIG_NUMA
> >  	s->remote_node_defrag_ratio = 1000;
> >
> 
> Move the ilog2 use into calculate_min_partial()? Otherweise
> calculate_min_partial is merely enforcing limits and not doing any
> calculations.
> 

The second patch in this series as a /sys/kernel/slab/cache/min_partial 
tunable that uses calculate_min_partial() to enforce a sane range, so 
while it may not actually be doing any calculations, the ilog2() is 
appropriately placed in kmem_cache_open().  We don't want to be taking the 
log of the user's min_partial value.
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