linux-kernel - Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86

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Message-ID: <4A4A9D8E.5080500@zytor.com>
Date:	Tue, 30 Jun 2009 16:19:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Mikael Pettersson <mikpe@...uu.se>,
	Matthew Wilcox <matthew@....cx>,
	Grant Grundler <grundler@...isc-linux.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit
 x86

Yinghai Lu wrote:
> Linus Torvalds wrote:
>> On Tue, 30 Jun 2009, Linus Torvalds wrote:
>>> I don't see any single-use trick then, and so it needs the whole statement 
>>> expression mess.
>> Hmm. Does (((x)-1) | mask)+1) work?
>>
>> I haven't thought it fully through, but that _should_ take care of the 
>> "already aligned" case, no?
> 
> yes. that is right.
> 
> then how about
> roundup(x,y)
> round_up(x,y)
> 
> roundup doesn't need y is 2^n
> but round_up does need y is 2^n, and only for x86
> 

We should definitely move whatever to global.  However, I do think it is
valuable to have something that can avoid divides even if the argument
is not necessarily a constant.

	-hpa
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