Re: 2G memory split

From: Mark Lord
Date: Mon Apr 10 2006 - 10:40:47 EST


Kirill Korotaev wrote:
+#if defined(CONFIG_DEFAULT_3G)
+#define __PAGE_OFFSET_RAW (0xC0000000)
+#elif defined(CONFIG_DEFAULT_3G_OPT)
+#define __PAGE_OFFSET_RAW (0xB0000000)
+#elif defined(CONFIG_DEFAULT_2G)
+#define __PAGE_OFFSET_RAW (0x78000000)
+#elif defined(CONFIG_DEFAULT_1G)
+#define __PAGE_OFFSET_RAW (0x40000000)
+#else
+#error "Bad user/kernel offset"
+#endif
+
#ifdef __ASSEMBLY__
-#define __PAGE_OFFSET (0xC0000000)
+#define __PAGE_OFFSET __PAGE_OFFSET_RAW
#define __PHYSICAL_START CONFIG_PHYSICAL_START
#else
-#define __PAGE_OFFSET (0xC0000000UL)
+#define __PAGE_OFFSET ((unsigned long)__PAGE_OFFSET_RAW)
#define __PHYSICAL_START ((unsigned long)CONFIG_PHYSICAL_START)
#endif
#define __KERNEL_START (__PAGE_OFFSET + __PHYSICAL_START)

Changing PAGE_OFFSET this way would break at least Valgrind (the latest
release 3.1.0 by default is statically linked at address 0xb0000000, and
PIE support does not seem to be present in that release). I remember
that similar changes were also breaking Lisp implementations (cmucl,
sbcl), however, I am not really sure about this.
it also breaks some java versions, so we use 3:4 Gb split in OpenVZ, but redhat still uses 4:4 in enterprise version, so number of such applications should decrease :)

Mmm.. that's an old thread. The reply above was to
a posting from Sergey Vlasov (the same) on Tue Jan 10 2006,
12:06:50 EST.
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