Re: [RFC/RFT] swsusp: image size tunable (was: Re: [PATCH][mm] swsusp: limit image size)

[Pavel Machek <pavel@suse.cz>]

Hi!

> > The tunable may be useful to people who'd like to achieve the
> > maximum efficiency of suspend/resume and it would be a nice
> > feature to have, I think, but let's say we'll try to implement it
> > in the future, if still needed/wanted.
> 
> Actually the tunable turned out to be quite easy to implement and I think
> I'll need it for userspace swsusp (the suspend-handling userspace
> process will need to tell the kernel how much space there is for the
> image).

Looks mostly okay to me, small comments below.

> Index: linux-2.6.15-rc5-mm1/kernel/power/disk.c
> ===================================================================
> --- linux-2.6.15-rc5-mm1.orig/kernel/power/disk.c	2005-12-10 13:12:18.000000000 +0100
> +++ linux-2.6.15-rc5-mm1/kernel/power/disk.c	2005-12-10 13:20:38.000000000 +0100
> @@ -367,9 +367,34 @@
>  
>  power_attr(resume);
>  
> +static ssize_t image_size_show(struct subsystem * subsys, char *buf)
> +{
> +	return sprintf(buf, "%u\n", image_size);
> +}
> +
> +static ssize_t image_size_store(struct subsystem * subsys, const char * buf, size_t n)
> +{
> +	int len;
> +	char *p;
> +	unsigned int size;
> +
> +	p = memchr(buf, '\n', n);
> +	len = p ? p - buf : n;

len and p are unused.

> +	if (sscanf(buf, "%u", &size) == 1) {
> +		image_size = size < MAX_IMAGE_SIZE ? size : MAX_IMAGE_SIZE;
> +		return n;

Why the limit? We may want to allow very big images when someone wants
"as similar to suspended system as possible".

> Index: linux-2.6.15-rc5-mm1/kernel/power/power.h
> ===================================================================
> --- linux-2.6.15-rc5-mm1.orig/kernel/power/power.h	2005-12-10 13:12:18.000000000 +0100
> +++ linux-2.6.15-rc5-mm1/kernel/power/power.h	2005-12-10 13:20:46.000000000 +0100
> @@ -53,10 +53,12 @@
>  extern struct pbe *pagedir_nosave;
>  
>  /*
> - * Preferred image size in MB (set it to zero to get the smallest
> + * Maximum image size in MB (set it to zero to get the smallest
>   * image possible)
>   */

In fact this is not maximum. If more than 500MB can't be freed, well,
it will not be freed. Very improbable, but possible.

> -#define IMAGE_SIZE	500
> +#define MAX_IMAGE_SIZE	500
> +

With runtime configuration, we should not need additional
compile-time config. OTOH /proc tunables should have descritption in
Documentation/.

								Pavel
-- 
Thanks, Sharp!