linux-kernel - [PATCH] x86: suggest running a 64bit kernel on LM capable machines with plenty memory.

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Date:	Mon, 09 Mar 2009 14:42:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ozan Çağlayan <ozan@...dus.org.tr>,
	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] x86: suggest running a 64bit kernel on LM capable machines
 with plenty memory.

On Sun, 2009-03-08 at 21:20 +0100, Andi Kleen wrote:
> Ozan Çağlayan <ozan@...dus.org.tr> writes:
> >
> > So, the PAE enabled kernel should be installed by distribution installers or
> > package management systems if the processor honors the PAE bit. Because PAE
> > is an extension mechanism for 32bit processors, AFAIK it has some overhead.
> > So enabling it if the user doesn't have a memory size >=4GB would not make
> > much sense if a proper noexecute (NX) support is not intended.
> 
> The general recommendation is to always use PAE when the machine 
> is NX capable. Or at least use it by default.

How about we do the below as well?

---
If the hardware is capable, its much better to run a 64bit kernel than a
32bit PAE kernel with lots of memory.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 arch/x86/mm/init_32.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 34ef5c7..3d22baa 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -714,6 +714,9 @@ void __init lowmem_pfn_init(void)
 
 #define MSG_HIGHMEM_TRIMMED \
 	"Warning: only 4GB will be used. Use a HIGHMEM64G enabled kernel!\n"
+
+#define MSG_LM_TRIMMED \
+	"Warning: instead of using a 32bit PAE kernel, Use a 64bit kernel!\n"
 /*
  * We have more RAM than fits into lowmem - we try to put it into
  * highmem, also taking the highmem=x boot parameter into account:
@@ -750,6 +753,8 @@ void __init highmem_pfn_init(void)
 	}
 #endif /* !CONFIG_HIGHMEM64G */
 #endif /* !CONFIG_HIGHMEM */
+	if (boot_cpu_has(X86_FEATURE_LM))
+		printk(KERN_WARNING MSG_LM_TRIMMED);
 }
 
 /*


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