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

To: xfs@xxxxxxxxxxx
Subject: Re: block sizes > 4K ?? possible w/large page support?
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Mon, 11 Jun 2012 09:54:57 -0500
In-reply-to: <20120611132932.GA18432@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <4FD5643F.5070801@xxxxxxxxx> <20120611132932.GA18432@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Reply-to: stan@xxxxxxxxxxxxxxxxx
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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?

-- 
Stan

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