[PATCH 1/2] Populate rootfs asynchronously for boot performance

[Andy Whitcroft]

On Mon, Dec 07, 2009 at 07:32:06PM +0200, Surbhi Palande wrote:
> populate_rootfs() is called asynchronously to reduce the boot time.
> 
> Signed-off-by: Surbhi Palande <surbhi.palande at canonical.com>
> ---
>  init/initramfs.c |   15 ++++++++++++---
>  init/main.c      |    7 +++++++
>  2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/init/initramfs.c b/init/initramfs.c
> index 4c00edc..aad2c28 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -8,6 +8,7 @@
>  #include <linux/dirent.h>
>  #include <linux/syscalls.h>
>  #include <linux/utime.h>
> +#include <linux/async.h>
>  
>  static __initdata char *message;
>  static void __init error(char *x)
> @@ -565,7 +566,9 @@ static void __init clean_rootfs(void)
>  }
>  #endif
>  
> -static int __init populate_rootfs(void)
> +extern struct list_head rootfs_fn_list;

Externs are frowned upon heavily in .c files, as it is possible to get
an undetected type missmatch leading to unexpected behaviour.  You
should move the extern to a header that these two files both include,
there is likely something already.  Also I would rather see the
declaration here in this file as its the primary consumer of it.

I also think the name is a bit wierd, as its not a function list?  If
anything its an async_t list, but you are not meant to know that, its an
opaque type.  populate_rootfs_domain or something seems more sensible to
my eye.

> +
> +static void __init async_populate_rootfs(void)
>  {
>  	char *err = unpack_to_rootfs(__initramfs_start,
>  			 __initramfs_end - __initramfs_start);
> @@ -579,7 +582,7 @@ static int __init populate_rootfs(void)
>  			initrd_end - initrd_start);
>  		if (!err) {
>  			free_initrd();
> -			return 0;
> +			return;
>  		} else {
>  			clean_rootfs();
>  			unpack_to_rootfs(__initramfs_start,
> @@ -603,6 +606,12 @@ static int __init populate_rootfs(void)
>  		free_initrd();
>  #endif
>  	}
> -	return 0;
> +	return;
>  }
> +
> +static int __init populate_rootfs(void)
> +{
> +	async_schedule_domain(async_populate_rootfs, NULL, &rootfs_fn_list);
> +}
> +
>  rootfs_initcall(populate_rootfs);
> diff --git a/init/main.c b/init/main.c
> index 4051d75..d40ca6f 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -752,6 +752,7 @@ int do_one_initcall(initcall_t fn)
>  
>  
>  extern initcall_t __initcall_start[], __initcall_end[], __early_initcall_end[];
> +LIST_HEAD(rootfs_fn_list);
>  
>  static void __init do_initcalls(void)
>  {
> @@ -879,6 +880,12 @@ static int __init kernel_init(void * unused)
>  	do_basic_setup();
>  
>  	/*
> +	 * putting it here to ensure that rootfs is populated by the end of

putting it here?

/* 
 * We need to ensure the filesystem is ready by this point, wait for
 * async_populate_rootfs to complete.
 */

> +	 * this call
> +	 */
> +	async_synchronize_full_domain(&rootfs_fn_list);
> +
> +	/*
>  	 * check if there is an early userspace init.  If yes, let it do all
>  	 * the work
>  	 */

-apw