linux-kernel - Re: [PATCH] Documentation: vm: Add 1GB large page support information

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Message-ID: <CALLJCT0fofgUaswpzt1iBqGS1u+fR8L=umwGpV=RG0SvO9TOJA@mail.gmail.com>
Date:	Thu, 6 Nov 2014 00:21:14 +0900
From:	Masanari Iida <standby24x7@...il.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Jonathan Corbet <corbet@....net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, lcapitulino@...hat.com
Subject: Re: [PATCH] Documentation: vm: Add 1GB large page support information

Luiz, Dave,
Thanks for comments.

I understand that there are some exception cases which doesn't support 1G
large pages on newer CPUs.
I like Dave's example, at the same time I would like to add "pdpe1gb flag" in
the document.

For example, x86 CPUs normally support 4K and 2M (1G if pdpe1gb flag exist).

Masanari

On Tue, Nov 4, 2014 at 3:18 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 10/31/2014 09:01 AM, Masanari Iida wrote:
>> --- a/Documentation/vm/hugetlbpage.txt
>> +++ b/Documentation/vm/hugetlbpage.txt
>> @@ -2,7 +2,8 @@
>>  The intent of this file is to give a brief summary of hugetlbpage support in
>>  the Linux kernel.  This support is built on top of multiple page size support
>>  that is provided by most modern architectures.  For example, i386
>> -architecture supports 4K and 4M (2M in PAE mode) page sizes, ia64
>> +architecture supports 4K and 4M (2M in PAE mode) page sizes, x86_64
>> +architecture supports 4K, 2M and 1G (SandyBridge or later) page sizes. ia64
>>  architecture supports multiple page sizes 4K, 8K, 64K, 256K, 1M, 4M, 16M,
>>  256M and ppc64 supports 4K and 16M.  A TLB is a cache of virtual-to-physical
>>  translations.  Typically this is a very scarce resource on processor.
>
> I wouldn't mention SandyBridge.  Not all x86 CPUs are Intel. :)
>
> Also, what of the Intel CPUs like the Xeon Phi or the Atom cores?  I
> have an IvyBridge (>= Sandybridge) mobile CPU in this laptop which does
> not support 1G pages.
>
> I would axe the i386-specific reference and just say something generic like:
>
>        For example, x86 CPUs normally support 4K and 2M (1G sometimes).
>
>
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