[PATCH] shrink VFS hash sizes on small machines

From: Matt Mackall <mpm@selenic.com>

Base hash sizes on available memory rather than total memory.  An
additional 50% above current used memory is considered reserved for the
purposes of hash sizing to compensate for the hashes themselves and the
remainder of kernel and userspace initialization.

fs/dcache.c

@@ -28,6 +28,7 @@
 #include <asm/uaccess.h>
 #include <linux/security.h>
 #include <linux/seqlock.h>
+#include <linux/swap.h>
 
 #define DCACHE_PARANOIA 1
 /* #define DCACHE_DEBUG 1 */
@@ -1619,6 +1620,14 @@ extern void chrdev_init(void);
 
 void __init vfs_caches_init(unsigned long mempages)
 {
+	unsigned long reserve;
+
+	/* Base hash sizes on available memory, with a reserve equal to
+           150% of current kernel size */
+
+	reserve = (mempages - nr_free_pages()) * 3/2;
+	mempages -= reserve;
+
 	names_cachep = kmem_cache_create("names_cache",
 			PATH_MAX, 0,
 			SLAB_HWCACHE_ALIGN, NULL, NULL);