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

From: Rafael J. Wysocki
Date: Sun Jan 08 2012 - 16:28:21 EST

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On Friday, January 06, 2012, Barry Song wrote:
> 2012/1/6 Pavel Machek <pavel@xxxxxx>:
> > Hi!
> >
> > Is the check even useful these days? Should we remove it altogether?
>
> i think we can let users or distributions decide whether it is useful.
> On PC, disk space is not an issue, people might run many applications
> while doing hibernation, so snapshot is much big. an early check will
> improve user experience because people don't need to wait a long time
> and find space is not enough.
> for embedded system, SoC solutions can know whether the space is
> enough since they know what are running while doing hibernation, so
> they can skip the check by setting the flag in sysfs.
> that is why i had this patch sent.

I agree with Pavel that it's better to drop the check altogether.

The sysfs switch you're adding doesn't seem to be very useful, as PC
users won't touch it and whoever needs it to be 0, will always set it
that way and won't change it afterwards.

Thanks,
Rafael

> >> 2011/11/25 Barry Song <Barry.Song@xxxxxxx>:
> >> > From: Barry Song <baohua.song@xxxxxxx>
> >> >
> >> > 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@xxxxxxx>
> >> > Cc: Xiangzhen Ye <Xiangzhen.Ye@xxxxxxx>
> >> > ---
> >> > -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) ?
> >> > --
> >> > 1.7.1
> >
> -barry
>
>

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