linux-kernel - Re: [Bug fix PATCH 1/2] acpi, movablemem_map: Exclude memblock.reserved ranges when parsing SRAT.

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Date:	Wed, 20 Feb 2013 20:31:39 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	akpm@...ux-foundation.org, jiang.liu@...wei.com,
	wujianguo@...wei.com, hpa@...or.com, wency@...fujitsu.com,
	laijs@...fujitsu.com, linfeng@...fujitsu.com, yinghai@...nel.org,
	isimatu.yasuaki@...fujitsu.com, rob@...dley.net,
	kosaki.motohiro@...fujitsu.com, minchan.kim@...il.com,
	mgorman@...e.de, rientjes@...gle.com, guz.fnst@...fujitsu.com,
	rusty@...tcorp.com.au, lliubbo@...il.com, jaegeuk.hanse@...il.com,
	tony.luck@...el.com, glommer@...allels.com
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [Bug fix PATCH 1/2] acpi, movablemem_map: Exclude memblock.reserved
 ranges when parsing SRAT.

On 02/20/2013 07:00 PM, Tang Chen wrote:
> As mentioned by HPA before, when we are using movablemem_map=acpi, if all the
> memory ranges in SRAT is hotpluggable, then no memory can be used by kernel.
>
> Before parsing SRAT, memblock has already reserve some memory ranges for other
> purposes, such as for kernel image, and so on. We cannot prevent kernel from
> using these memory. So we need to exclude these ranges even if these memory is
> hotpluggable.
>
> This patch changes the movablemem_map=acpi option's behavior. The memory ranges
> reserved by memblock will not be added into movablemem_map.map[]. So even if
> all the memory is hotpluggable, there will always be memory that could be used
> by the kernel.
>
> Reported-by: H Peter Anvin<hpa@...or.com>
> Signed-off-by: Tang Chen<tangchen@...fujitsu.com>
> ---
>   arch/x86/mm/srat.c |   18 +++++++++++++++++-
>   1 files changed, 17 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
> index 62ba97b..b8028b2 100644
> --- a/arch/x86/mm/srat.c
> +++ b/arch/x86/mm/srat.c
> @@ -145,7 +145,7 @@ static inline int save_add_info(void) {return 0;}
>   static void __init
>   handle_movablemem(int node, u64 start, u64 end, u32 hotpluggable)
>   {
> -	int overlap;
> +	int overlap, i;
>   	unsigned long start_pfn, end_pfn;
>
>   	start_pfn = PFN_DOWN(start);
> @@ -161,8 +161,24 @@ handle_movablemem(int node, u64 start, u64 end, u32 hotpluggable)
>   	 *
>   	 * Using movablemem_map, we can prevent memblock from allocating memory
>   	 * on ZONE_MOVABLE at boot time.
> +	 *
> +	 * Before parsing SRAT, memblock has already reserve some memory ranges
> +	 * for other purposes, such as for kernel image. We cannot prevent
> +	 * kernel from using these memory, so we need to exclude these memory
> +	 * even if it is hotpluggable.
>   	 */
>   	if (hotpluggable&&  movablemem_map.acpi) {
> +		/* Exclude ranges reserved by memblock. */
> +		struct memblock_type *rgn =&memblock.reserved;
> +
> +		for (i = 0; i<  rgn->cnt; i++) {
> +			if (end<= rgn->regions[i].base ||
> +			    start>= rgn->regions[i].base +
> +			    rgn->regions[i].size)

Hi all,

Here, I scan the memblock.reserved each time we parse an entry because the
rgn->regions[i].nid is set to MAX_NUMNODES in memblock_reserve(). So I 
cannot
obtain the nid which the kernel resides in directly from memblock.reserved.

I think there could be some problems if the memory ranges in SRAT are not in
increasing order, since if [3,4) [1,2) are all on node0, and kernel is not
using [3,4), but using [1,2), then I cannot remove [3,4) because I don't 
know
on which node [3,4) is.

Any idea for this ?

And by the way, I think this approach works well when the memory entries in
SRAT are arranged in increasing order.

Thanks. :)

> +				continue;
> +			goto out;
> +		}
> +
>   		insert_movablemem_map(start_pfn, end_pfn);
>
>   		/*
--
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