linux-kernel - Re: [PATCH 07/11] x86, memblock: Set lowest limit for memblock_alloc_base

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Date:	Tue, 03 Sep 2013 18:37:21 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	rjw@...k.pl, lenb@...nel.org, tglx@...utronix.de, mingo@...e.hu,
	hpa@...or.com, akpm@...ux-foundation.org, tj@...nel.org,
	trenn@...e.de, yinghai@...nel.org, jiang.liu@...wei.com,
	wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, zhangyanfei@...fujitsu.com, x86@...nel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 07/11] x86, memblock: Set lowest limit for
 memblock_alloc_base_nid().

On Tue, 2013-08-27 at 17:37 +0800, Tang Chen wrote:
> memblock_alloc_base_nid() is a common API of memblock. And it calls
> memblock_find_in_range_node() with %start = 0, which means it has no
> limit for the lowest address by default.
> 
> 	memblock_find_in_range_node(0, max_addr, size, align, nid);
> 
> Since we introduced current_limit_low to memblock, if we have no limit
> for the lowest address or we are not sure, we should pass
> MEMBLOCK_ALLOC_ACCESSIBLE to %start so that it will be limited by the
> default low limit.
> 
> dma_contiguous_reserve() and setup_log_buf() will eventually call
> memblock_alloc_base_nid() to allocate memory. So if the allocation order
> is from low to high, they will allocate memory from the lowest limit
> to higher memory.

This requires the callers to use MEMBLOCK_ALLOC_ACCESSIBLE instead of 0.
Is there a good way to make sure that all callers will follow this rule
going forward?  Perhaps, memblock_find_in_range_node() should emit some
message if 0 is passed when current_order is low to high and the boot
option is specified?

Similarly, I wonder if we should have a check to the allocation size to
make sure that all allocations will stay small in this case.

Thanks,
-Toshi


> 
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> Reviewed-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>
> ---
>  mm/memblock.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 961d4a5..be8c4d1 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -851,7 +851,8 @@ static phys_addr_t __init memblock_alloc_base_nid(phys_addr_t size,
>  	/* align @size to avoid excessive fragmentation on reserved array */
>  	size = round_up(size, align);
>  
> -	found = memblock_find_in_range_node(0, max_addr, size, align, nid);
> +	found = memblock_find_in_range_node(MEMBLOCK_ALLOC_ACCESSIBLE,
> +					    max_addr, size, align, nid);
>  	if (found && !memblock_reserve(found, size))
>  		return found;
>  


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