[PATCH v2] PM: HIBERNATION: skip the swap size check if the snapshot image size is anticipative

[matthieu.castet@parrot.com (Matthieu CASTET)]

Hi,

but did embedded system will really use swap interface ?

Often they don't have swap and can already save suspend image in disk/nand :
- SNAPSHOT_CREATE_IMAGE
- read it from /dev/snapshot and write it to a file.

The only problem with the current interface, is that you can't SNAPSHOT_UNFREEZE
before reading the image.
But this is need for some filesystem that have thread.


For example we have a demo where we save the suspend image in a ubi volume and
restore it from bootloader.


Matthieu

Barry Song a ?crit :
> From: Barry Song <baohua.song@csr.com>
> 
> Current swsusp requires swap partitions even larger than real saved pages
> based on the worst compression ratio:
> but for an embedded system, which has limited storage space, then it might
> can't give the large partition to save snapshot.
> In the another way, some embedded systems can definitely know the most size
> needed for snapshot since they run some specific application lists.
> So this patch provides the possibility for users to tell kernel even
> the system has a little snapshot partition, but it is still enough.
> For example, if the system need to save 120MB memory, origin swsusp will require
> a 130MB partition to save snapshot. but if users know 30MB is enough for them(
> compressed image will be less than 30MB), they just make a 30MB partition by
> echo 0 > /sys/power/check_swap_size
> 
> Signed-off-by: Barry Song <Baohua.Song@csr.com>
> Cc: Xiangzhen Ye <Xiangzhen.Ye@csr.com>
> ---
>  -v2:drop swap_enough bootargs and use /sys/power/check_swap_size node
> 
>  Documentation/power/interface.txt |    5 +++++
>  kernel/power/hibernate.c          |   22 ++++++++++++++++++++++
>  kernel/power/power.h              |    2 ++
>  kernel/power/swap.c               |    9 +++++++++
>  4 files changed, 38 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt
> index c537834..5e205f0 100644
> --- a/Documentation/power/interface.txt
> +++ b/Documentation/power/interface.txt
> @@ -47,6 +47,11 @@ Writing to this file will accept one of
>         'testproc'
>         'test'
>  
> +/sys/power/check_swap_size controls whether we can skip checking the swap
> +partition size by worst compression ratio. If users know the swap partition
> +is enough for compressed snapshot, write 0 to /sys/power/check_swap_size.
> +It is useful for an embedded system with known running softwares.
> +
>  /sys/power/image_size controls the size of the image created by
>  the suspend-to-disk mechanism.  It can be written a string
>  representing a non-negative integer that will be used as an upper
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 1c53f7f..5552473 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1024,11 +1024,33 @@ static ssize_t reserved_size_store(struct kobject *kobj,
>  
>  power_attr(reserved_size);
>  
> +static ssize_t check_swap_size_show(struct kobject *kobj, struct kobj_attribute *attr,
> +			       char *buf)
> +{
> +	return sprintf(buf, "%d\n", check_swap_size);
> +}
> +
> +static ssize_t check_swap_size_store(struct kobject *kobj, struct kobj_attribute *attr,
> +				const char *buf, size_t n)
> +{
> +	int check_size;
> +
> +	if (sscanf(buf, "%d", &check_size) == 1) {
> +		check_swap_size = check_size;
> +		return n;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +power_attr(check_swap_size);
> +
>  static struct attribute * g[] = {
>  	&disk_attr.attr,
>  	&resume_attr.attr,
>  	&image_size_attr.attr,
>  	&reserved_size_attr.attr,
> +	&check_swap_size_attr.attr,
>  	NULL,
>  };
>  
> diff --git a/kernel/power/power.h b/kernel/power/power.h
> index 23a2db1..4f0fa78 100644
> --- a/kernel/power/power.h
> +++ b/kernel/power/power.h
> @@ -74,6 +74,8 @@ static struct kobj_attribute _name##_attr = {	\
>  
>  /* Preferred image size in bytes (default 500 MB) */
>  extern unsigned long image_size;
> +/* If 0, skip checking whether the swap size is enough for compressed snapshot */
> +extern int check_swap_size;
>  /* Size of memory reserved for drivers (default SPARE_PAGES x PAGE_SIZE) */
>  extern unsigned long reserved_size;
>  extern int in_suspend;
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 11a594c..db90195 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -37,6 +37,12 @@
>  #define HIBERNATE_SIG	"S1SUSPEND"
>  
>  /*
> + * if users know swap partitions are enough for compressed snapshots,
> + * echo 0 > /sys/power/check_swap_size
> + */
> +int check_swap_size = 1;
> +
> +/*
>   *	The swap map is a data structure used for keeping track of each page
>   *	written to a swap partition.  It consists of many swap_map_page
>   *	structures that contain each an array of MAP_PAGE_ENTRIES swap entries.
> @@ -772,6 +778,9 @@ static int enough_swap(unsigned int nr_pages, unsigned int flags)
>  	unsigned int free_swap = count_swap_pages(root_swap, 1);
>  	unsigned int required;
>  
> +	if (!check_swap_size)
> +		return 1;
> +
>  	pr_debug("PM: Free swap pages: %u\n", free_swap);
>  
>  	required = PAGES_FOR_IO + ((flags & SF_NOCOMPRESS_MODE) ?