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

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Message-ID: <4F9B5387.8030002@intel.com>
Date:	Sat, 28 Apr 2012 10:18:47 +0800
From:	ShuoX Liu <shuox.liu@...el.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Yanmin Zhang <yanmin_zhang@...ux.intel.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>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] percpu, x86: don't use PMD_SIZE as embedded atom_size
 on 32bit

On 2012年04月28日 00:53, 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 later atom_size reportedly leads to frequent
> percpu allocation failures on certain setups.
> 
> This patch makes x86_32 always use PAGE_SIZE as atom_size for embed
> first chunk allocator.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Yanmin Zhang <yanmin.zhang@...el.com>
> Reported-by: ShuoX Liu <shuox.liu@...el.com>
> LKML-Reference: <4F97BA98.6010001@...el.com>
> Cc: stable@...r.kernel.org
> ---
> Can you please verify this resolves the issue you guys are seeing?
> Once verified, I'll push it through percpu/for-3.5-fixes.
> 

Verify OK.

> Thanks.
> 
>  arch/x86/kernel/setup_percpu.c |   14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
> index 71f4727..ed96573 100644
> --- a/arch/x86/kernel/setup_percpu.c
> +++ b/arch/x86/kernel/setup_percpu.c
> @@ -185,10 +185,22 @@ void __init setup_per_cpu_areas(void)
>  #endif
>  	rc = -EINVAL;
>  	if (pcpu_chosen_fc != PCPU_FC_PAGE) {
> -		const size_t atom_size = cpu_has_pse ? PMD_SIZE : PAGE_SIZE;
>  		const size_t dyn_size = PERCPU_MODULE_RESERVE +
>  			PERCPU_DYNAMIC_RESERVE - PERCPU_FIRST_CHUNK_RESERVE;
> +		size_t atom_size;
>  
> +		/*
> +		 * 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
>  		rc = pcpu_embed_first_chunk(PERCPU_FIRST_CHUNK_RESERVE,
>  					    dyn_size, atom_size,
>  					    pcpu_cpu_distance,


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