[PATCH] Add retain_initrd boot option

[Michael Neuling <mikey@neuling.org>]

Add retain_initrd option to control freeing of initrd memory after
extraction.  By default, free memory as previously. 

The first boot will need to hold a copy of the in memory fs for the
second boot.  This image can be large (much larger than the kernel),
hence we can save time when the memory loader is slow.  Also, it reduces
the memory footprint while extracting the first boot since you don't
need another copy of the fs.

Signed-off-by: Michael Neuling <mikey@neuling.org>
---
Updated to work when CONFIG_KEXEC=n, as spotted by Randy Dunlap.

 Documentation/kernel-parameters.txt |    2 ++
 init/initramfs.c                    |   17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

Index: linux-2.6-ozlabs/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6-ozlabs.orig/Documentation/kernel-parameters.txt
+++ linux-2.6-ozlabs/Documentation/kernel-parameters.txt
@@ -1366,6 +1366,8 @@ and is between 256 and 4096 characters. 
 	resume=		[SWSUSP]
 			Specify the partition device for software suspend
 
+	retain_initrd	[RAM] Keep initrd memory after extraction
+
 	rhash_entries=	[KNL,NET]
 			Set number of hash buckets for route cache
 
Index: linux-2.6-ozlabs/init/initramfs.c
===================================================================
--- linux-2.6-ozlabs.orig/init/initramfs.c
+++ linux-2.6-ozlabs/init/initramfs.c
@@ -487,6 +487,17 @@ static char * __init unpack_to_rootfs(ch
 	return message;
 }
 
+static int do_retain_initrd;
+
+static int __init retain_initrd_param(char *str)
+{
+	if (*str)
+		return 0;
+	do_retain_initrd = 1;
+	return 1;
+}
+__setup("retain_initrd", retain_initrd_param);
+
 extern char __initramfs_start[], __initramfs_end[];
 #ifdef CONFIG_BLK_DEV_INITRD
 #include <linux/initrd.h>
@@ -497,7 +508,11 @@ static void __init free_initrd(void)
 #ifdef CONFIG_KEXEC
 	unsigned long crashk_start = (unsigned long)__va(crashk_res.start);
 	unsigned long crashk_end   = (unsigned long)__va(crashk_res.end);
+#endif
+	if (do_retain_initrd)
+		goto skip;
 
+#ifdef CONFIG_KEXEC
 	/*
 	 * If the initrd region is overlapped with crashkernel reserved region,
 	 * free only memory that is not part of crashkernel region.
@@ -515,7 +530,7 @@ static void __init free_initrd(void)
 	} else
 #endif
 		free_initrd_mem(initrd_start, initrd_end);
-
+skip:
 	initrd_start = 0;
 	initrd_end = 0;
 }