linux-kernel - Re: [PATCH 2/2] x86,mm,64bit: Round up memory boundary for init_memory_mapping

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Message-ID: <4D680EA4.6050402@kernel.org>
Date:	Fri, 25 Feb 2011 12:18:44 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86,mm,64bit: Round up memory boundary for init_memory_mapping_high()

On 02/25/2011 03:16 AM, Tejun Heo wrote:
> On Thu, Feb 24, 2011 at 10:20:35PM -0800, Yinghai Lu wrote:
>> tj pointed out:
>> 	when node does not have 1G aligned boundary, like 128M.
>> init_memory_mapping_high() could render smaller mapping by 128M on one node,
>> and 896M on next node with 2M pages instead of 1g page. that could increase
>> TLB presure.
>>
>> So if gb page is used, try to align the boundary to 1G before calling
>> init_memory_mapping_ext(), to make sure only use one 1g entry for that cross
>> node 1G.
>> Need to init_meory_mapping_ext() to table tbl_end, to make sure pgtable is on
>> previous node instead of next node.
> 
> I don't know, Yinghai.  The whole code seems overly complicated to me.
> Just ignore e820 map when building linear mapping.  It doesn't matter.
> Why not just do something like the following?  Also, can you please
> add some comments explaining how the NUMA affine allocation actually
> works for page tables?
yes, that could be done in separated patch.

>  Or better, can you please make that explicit?
> It currently depends on memories being registered in ascending address
> order, right?  The memblock code already is NUMA aware, I think it
> would be far better to make the node affine part explicit.

yes, memblock is numa aware after memblock_x86_register_active_regions().
and it rely on early_node_map[].

do you mean let init_memory_mapping to take node id like setup_node_bootmem?
so find_early_table_space could take nodeid instead of tbl_end? 

> 
> Thanks.
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 46e684f..4fd0b59 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -966,6 +966,11 @@ void __init setup_arch(char **cmdline_p)
>  	memblock.current_limit = get_max_mapped();
>  
>  	/*
> +	 * Add whole lot of comment explaining what's going on and WHY
> +	 * because as it currently stands, it's frigging cryptic.
> +	 */
> +
> +	/*
>  	 * NOTE: On x86-32, only from this point on, fixmaps are ready for use.
>  	 */
>  
> diff --git a/arch/x86/mm/numa_64.c b/arch/x86/mm/numa_64.c
> index 7757d22..50ec03c 100644
> --- a/arch/x86/mm/numa_64.c
> +++ b/arch/x86/mm/numa_64.c
> @@ -536,8 +536,6 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
>  	if (!numa_meminfo_cover_memory(mi))
>  		return -EINVAL;
>  
> -	init_memory_mapping_high();
> -
>  	/* Finally register nodes. */
>  	for_each_node_mask(nid, node_possible_map) {
>  		u64 start = (u64)max_pfn << PAGE_SHIFT;
> @@ -550,8 +548,12 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
>  			end = max(mi->blk[i].end, end);
>  		}
>  
> -		if (start < end)
> +		if (start < end) {
> +			init_memory_mapping(
> +			  ALIGN_DOWN_TO_MAX_MAP_SIZE_AND_CONVERT_TO_PFN(start),
> +			  ALIGN_UP_SIMILARY_BUT_DONT_GO_OVER_MAX_PFN(end));
>  			setup_node_bootmem(nid, start, end);
> +		}
will have problem with cross node conf. like 0-4g, 8-12g on node0, 4g-8g, 12g-16g on node1.

>  	}
>  
>  	return 0;
> 
> 

Thanks

Yinghai Lu
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