linux-kernel - Re: [PATCH v2] percpu, x86: don't use PMD_SIZE as embedded atom

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Message-ID: <4F9ADCAF.5000203@zytor.com>
Date:	Fri, 27 Apr 2012 10:51:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Tejun Heo <tj@...nel.org>
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 v2] percpu, x86: don't use PMD_SIZE as embedded atom_size
 on 32bit

On 04/27/2012 10:39 AM, Tejun Heo wrote:
> With the embed percpu first chunk allocator, x86 uses either PAGE_SIZE
> or PMD_SIZE for atom_size.  PMD_SIZE is used when CPU supports PSE so
> that percpu areas are aligned to PMD mappings and possibly allow using
> PMD mappings in vmalloc areas in the future.  Using larger atom_size
> doesn't waste actual memory; however, it does require larger vmalloc
> space allocation later on for !first chunks.
> 
> With reasonably sized vmalloc area, PMD_SIZE shouldn't be a problem
> but x86_32 at this point is anything but reasonable in terms of
> address space and using larger atom_size reportedly leads to frequent
> percpu allocation failures on certain setups.
> 
> As there is no reason to not use PMD_SIZE on x86_64 as vmalloc space
> is aplenty and most x86_64 configurations support PSE, fix the issue
> by always using PMD_SIZE on x86_64 and PAGE_SIZE on x86_32.
> 
> v2: drop cpu_has_pse test and make x86_64 always use PMD_SIZE and
>     x86_32 PAGE_SIZE as suggested by hpa.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Yanmin Zhang <yanmin.zhang@...el.com>
> Reported-by: ShuoX Liu <shuox.liu@...el.com>
> Acked-by: H. Peter Anvin <hpa@...or.com>
> LKML-Reference: <4F97BA98.6010001@...el.com>
> Cc: stable@...r.kernel.org

You're carrying this, or should I?

	-hpa

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