linux-kernel - Re: [PATCH] percpu, x86: don't use PMD_SIZE as embedded atom

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Message-ID: <20120427172731.GD26595@google.com>
Date:	Fri, 27 Apr 2012 10:27:31 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	ShuoX Liu <shuox.liu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] percpu, x86: don't use PMD_SIZE as embedded atom_size
 on 32bit

On Fri, Apr 27, 2012 at 10:17:17AM -0700, H. Peter Anvin wrote:
> On 04/27/2012 09:53 AM, Tejun Heo wrote:
> >  
> > +		/*
> > +		 * If PSE is available, use PMD_SIZE for atom_size so that
> > +		 * embedded percpu areas are aligned to PMD.  This, in the
> > +		 * future, can also allow using PMD mappings in vmalloc
> > +		 * area.  Use PAGE_SIZE on 32bit as vmalloc space is highly
> > +		 * contended and large vmalloc area alloc can easily fail.
> > +		 */
> > +		atom_size = PAGE_SIZE;
> > +#ifdef CONFIG_X86_64
> > +		if (cpu_has_pse)
> > +			atom_size = PMD_SIZE;
> > +#endif
> 
> Just make it PAGE_SIZE on i386 and PMD_SIZE on x86-64; keep the behavior
> consistent.  !cpu_has_pse on x86-64 is an abnormal situation (I think it
> applies to Xen, pretty much.)
> 
> Other than that,
> 
> Acked-by: H. Peter Anvin <hpa@...or.com>

Yeah, that's simpler.  Will update.

Thanks.

-- 
tejun
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