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Date: Fri, 27 Apr 2012 10:51:43 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Tejun Heo <tj@kernel.org>
CC: Yanmin Zhang <yanmin_zhang@linux.intel.com>,
        ShuoX Liu <shuox.liu@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Lameter <cl@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v2] percpu, x86: don't use PMD_SIZE as embedded atom_size
 on 32bit
References: <4F97BA98.6010001@intel.com> <20120425222429.GE8989@google.com> <1335405672.14538.135.camel@ymzhang.sh.intel.com> <20120426224946.GG27486@google.com> <1335488964.14538.159.camel@ymzhang.sh.intel.com> <1335516994.14538.160.camel@ymzhang.sh.intel.com> <20120427165356.GA26595@google.com> <20120427173935.GE26595@google.com>
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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@kernel.org>
> Reported-by: Yanmin Zhang <yanmin.zhang@intel.com>
> Reported-by: ShuoX Liu <shuox.liu@intel.com>
> Acked-by: H. Peter Anvin <hpa@zytor.com>
> LKML-Reference: <4F97BA98.6010001@intel.com>
> Cc: stable@vger.kernel.org

You're carrying this, or should I?

	-hpa