linux-kernel - Re: [patch 1/7] allocpercpu: Make it a true per cpu allocator by allocating from a per cpu array

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Message-ID: <Pine.LNX.4.64.0711010557340.27666@schroedinger.engr.sgi.com>
Date:	Thu, 1 Nov 2007 05:59:06 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	akpm@...ux-foundation.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [patch 1/7] allocpercpu: Make it a true per cpu allocator by
 allocating from a per cpu array

On Thu, 1 Nov 2007, Eric Dumazet wrote:

> Christoph Lameter a écrit :
> > +
> > +enum unit_type { FREE, END, USED };
> > +
> > +static u8 cpu_alloc_map[UNITS_PER_CPU] = { 1, };
> 
> You mean END here instead of 1 :)

Sigh. A leftover. This can be removed.

> > +/*
> > + * Allocate an object of a certain size
> > + *
> > + * Returns a per cpu pointer that must not be directly used.
> > + */
> > +static void *cpu_alloc(unsigned long size)
> > +{
> 
> We might need to give an alignment constraint here. Some per_cpu users would
> like to get a 64 bytes zone, siting in one cache line and not two :)

Well not sure about that. Alignment is mostly useful on SMP with cacheline 
contention. This is a per cpu area that should not be contended.