linux-kernel - Re: [PATCH 1/3] memblock, nobootmem: Add memblock_virt_alloc

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Date:	Fri, 24 Jan 2014 14:30:36 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Dave Hansen <dave.hansen@...el.com>,
	<linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 1/3] memblock, nobootmem: Add memblock_virt_alloc_low()

On Friday 24 January 2014 02:25 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 24, 2014 at 11:11:10AM -0800, Yinghai Lu wrote:
>> The new memblock_virt APIs are used to replaced old bootmem API.
>>
>> We need to allocate page below 4G for swiotlb.
>>
>> That should fix regression on Andrew's system that is using swiotlb.
> 
> Please include the title of the patch that caused the regression.
> I presume it is "mm/lib/swiotlb: Use memblock apis for early memory allocations"
> 
> Interestingly enough when I asked about it:
> 
> https://lkml.org/lkml/2013/11/9/280
> 
> 
> 	>> v_overflow_buffer = memblock_virt_alloc_align_nopanic(
> 	>> +						PAGE_ALIGN(io_tlb_overflow),
> 	>> +						PAGE_SIZE);
> 	> 
> 	> Does this guarantee that the pages will be allocated below 4GB?
> 	> 
> 	Yes. The memblock layer still allocates memory from lowmem. As I
> 	mentioned, there is no change in the behavior than what is today
> 	apart from just the interface change.
> 
> How did that happend? Was there another patch in the series that altered
> such assumption?
> 
Actually it didn't. It was the misunderstanding on my side about the
low_mem_max_addr being under 4GB, which is not always true especially
for 64-bit systems which have no addressing limitations. 

Regards,
Santosh

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