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Re: block sizes > 4K ?? possible w/large page support?

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: block sizes > 4K ?? possible w/large page support?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 12 Jun 2012 09:56:12 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4FD606C1.1070103@xxxxxxxxxxxxxxxxx>
References: <4FD5643F.5070801@xxxxxxxxx> <20120611132932.GA18432@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <4FD606C1.1070103@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Jun 11, 2012 at 09:54:57AM -0500, Stan Hoeppner wrote:
> On 6/11/2012 8:29 AM, Carlos Maiolino wrote:
> 
> > The maximum block size of a XFS filesystem is 64kiB. But in linux it's 
> > limited
> > to the PAGE_SIZE value. 
> 
> Correct.
> 
> > so, on x86 architectures, the maximum block size is
> > 4kiB.
> 
> Not entirely correct.  Since ~1996, 16 years ago, PPro and higher 32bit
> CPUs with PSE/PSE36 support pages of 4MB, or 2MB with PAE enabled.
> 
> x86-64 CPUs in long mode also support a 2MB page size.  But the problem
> of internal fragmentation may outweigh the TLB and other benefits of
> these very large pages.  I'm not an MM dev so I can't elaborate further.
>  There may be other issues.
> 
> > although it could benefit from a 16kiB page size, you'll need to be running 
> > an
> > operating system which supports this page size value.
> 
> And AFAIK the kernel MM team doesn't have x86 2MB pages on their radar.
>  Or do they?

Been supported for a few of years now in one form or another.
google for "transparent huge pages".....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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