linux-kernel - Re: [PATCH -mm 1/6] slab: introduce __kfree

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Date:	Mon, 23 Mar 2009 16:59:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 1/6] slab: introduce __kfree_rcu


* Christoph Lameter <cl@...ux-foundation.org> wrote:

> On Mon, 23 Mar 2009, Pekka Enberg wrote:
> 
> > > +static inline void *portion_to_obj(void *portion)
> > > +{
> > > +	struct page *page = virt_to_head_page(portion);
> > > +	struct slab *slab = page_get_slab(page);
> > > +	struct kmem_cache *cache = page_get_cache(page);
> > > +	unsigned int offset = portion - slab->s_mem;
> > > +	unsigned int index = offset / cache->buffer_size;
> > > +
> > > +	return index_to_obj(cache, slab, index);
> > > +}
> >
> > A minor nit: I think this would be more readable if you separated
> > variable declarations from the initializations. Also, you can probably
> > drop the inline from the function declaration and let GCC decide what to
> > do.
> 
> Thats debatable. I find the setting up a number of variables that 
> are all dependend in the above manner very readable. They are 
> usually repetitive. Multiple functions use similar 
> initializations.

I agree with Pekka, it's clearly more readable when separated out 
nicely:

	struct kmem_cache *cache;
	unsigned int offset;
	unsigned int index;
	struct page *page;
	struct slab *slab;

	page	= virt_to_head_page(portion);
	slab	= page_get_slab(page);
	cache	= page_get_cache(page);

	offset	= portion - slab->s_mem;
	index	= offset / cache->buffer_size;

The original form is hard to read due to lack of structure.

	Ingo
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