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From 9c50553cb28d0543e983b17b515f50dc5b57d21e Mon Sep 17 00:00:00 2001
From: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Date: Thu, 9 Sep 2010 21:13:28 +0200
Subject: [PATCH] x86: Limit 32bit PAE memory to 16G
commit 2da92b60dd58ce7613a909165cbd84cb69217b7d in tip.
This patch limits the amount of usable physical RAM to 16 GB on
i386. It solves bug 311411 "[RHEL5 RT] Kernel panic - not syncing: Out
of memory".
The crash was caused by running out of low memory while allocating the
memory map on machines equipped with more than ~56 GB RAM. The realtime
kernel does not like having too much RAM because it has larger struct
page then the normal kernel.
The officially supported amount of RAM on i386 RHEL-5 is 16 GB anyway.
Originally-From: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Clark Williams <williams@redhat.com>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
arch/x86/include/asm/setup.h | 1 +
arch/x86/kernel/e820.c | 11 +++++++++++
2 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 86b1506..efaa903 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -13,6 +13,7 @@
*/
#define MAXMEM_PFN PFN_DOWN(MAXMEM)
#define MAX_NONPAE_PFN (1 << 20)
+#define MAX_SANE_PAE_PFN (1 << 22)
#endif /* __i386__ */
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 7bca3c6..77a635e 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -871,6 +871,17 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, unsigned type)
if (start_pfn >= limit_pfn)
continue;
+#ifdef CONFIG_X86_32
+ if (end_pfn > MAX_SANE_PAE_PFN) {
+ last_pfn = MAX_SANE_PAE_PFN;
+ printk(KERN_WARNING
+ "WARNING: Running a 32 bit kernel with more "
+ "than 16 GB RAM is not supported on MRG RT.\n"
+ "Using only 16 GB. To take advantage of all "
+ "of your RAM, use a x86_64 kernel.\n");
+ break;
+ }
+#endif
if (end_pfn > limit_pfn) {
last_pfn = limit_pfn;
break;
--
1.7.0.4
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