[PATCH] shrink the amount of vmalloc space reserved for kmap

Patch from Manfred Spraul <manfred@colorfullife.com>

Effectively adds another 24 megabytes of ia32 KVA.

kmap uses a 4 MB (2 MB if PAE is enabled) area for the persistant mappings.
But PKMAP_BASE is 4GB-32MB, i.e.  around 28 MB are reserved for kmap (4 MB
for fixmappings).

The attached patch shrink that to 4 MB (+4MB for fixmappings) and adds a test
to check for an overlap between fixmap and kmap areas.

arch/i386/mm/init.c

@@ -438,6 +438,16 @@ void __init mem_init(void)
 	
 	bad_ppro = ppro_with_ram_bug();
 
+#ifdef CONFIG_HIGHMEM
+	/* check that fixmap and pkmap do not overlap */
+	if (PKMAP_BASE+LAST_PKMAP*PAGE_SIZE >= FIXADDR_START) {
+		printk(KERN_ERR "fixmap and kmap areas overlap - this will crash\n");
+		printk(KERN_ERR "pkstart: %lxh pkend: %lxh fixstart %lxh\n",
+				PKMAP_BASE, PKMAP_BASE+LAST_PKMAP*PAGE_SIZE, FIXADDR_START);
+		BUG();
+	}
+#endif
+ 
 	set_max_mapnr_init();
 
 #ifdef CONFIG_HIGHMEM

include/asm-i386/highmem.h

@@ -39,7 +39,7 @@ extern void kmap_init(void);
  * easily, subsequent pte tables have to be allocated in one physical
  * chunk of RAM.
  */
-#define PKMAP_BASE (0xfe000000UL)
+#define PKMAP_BASE (0xff800000UL)
 #ifdef CONFIG_X86_PAE
 #define LAST_PKMAP 512
 #else