PM / Hibernate: Add sysfs knob to control size of memory for drivers

Martin reports that on his system hibernation occasionally fails due
to the lack of memory, because the radeon driver apparently allocates
too much of it during the device freeze stage. It turns out that the
amount of memory allocated by radeon during hibernation (and
presumably during system suspend too) depends on the utilization of
the GPU (e.g. hibernating while there are two KDE 4 sessions with
compositing enabled causes radeon to allocate more memory than for
one KDE 4 session).

In principle it should be possible to use image_size to make the
memory preallocation mechanism free enough memory for the radeon
driver, but in practice it is not easy to guess the right value
because of the way the preallocation code uses image_size. For this
reason, it seems reasonable to allow users to control the amount of
memory reserved for driver allocations made after the hibernate
preallocation, which currently is constant and amounts to 1 MB.

Introduce a new sysfs file, /sys/power/reserved_size, whose value
will be used as the amount of memory to reserve for the
post-preallocation reservations made by device drivers, in bytes.
For backwards compatibility, set its default (and initial) value to
the currently used number (1 MB).

References: https://bugzilla.kernel.org/show_bug.cgi?id=34102
Reported-and-tested-by: Martin Steigerwald <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/ABI/testing/sysfs-power

···
 		successful, will make the kernel abort a subsequent transition
 		to a sleep state if any wakeup events are reported after the
 		write has returned.
+
+What:		/sys/power/reserved_size
+Date:		May 2011
+Contact:	Rafael J. Wysocki <[e-mail]>
+Description:
+		The /sys/power/reserved_size file allows user space to control
+		the amount of memory reserved for allocations made by device
+		drivers during the "device freeze" stage of hibernation.  It can
+		be written a string representing a non-negative integer that
+		will be used as the amount of memory to reserve for allocations
+		made by device drivers' "freeze" callbacks, in bytes.
+
+		Reading from this file will display the current value, which is
+		set to 1 MB by default.

kernel/power/hibernate.c

···
 
 power_attr(image_size);
 
+static ssize_t reserved_size_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", reserved_size);
+}
+
+static ssize_t reserved_size_store(struct kobject *kobj,
+				   struct kobj_attribute *attr,
+				   const char *buf, size_t n)
+{
+	unsigned long size;
+
+	if (sscanf(buf, "%lu", &size) == 1) {
+		reserved_size = size;
+		return n;
+	}
+
+	return -EINVAL;
+}
+
+power_attr(reserved_size);
+
 static struct attribute * g[] = {
 	&disk_attr.attr,
 	&resume_attr.attr,
 	&image_size_attr.attr,
+	&reserved_size_attr.attr,
 	NULL,
 };
 

kernel/power/main.c

···
 	if (error)
 		return error;
 	hibernate_image_size_init();
+	hibernate_reserved_size_init();
 	power_kobj = kobject_create_and_add("power", NULL);
 	if (!power_kobj)
 		return -ENOMEM;

kernel/power/power.h

···
 
 #ifdef CONFIG_HIBERNATION
 /* kernel/power/snapshot.c */
+extern void __init hibernate_reserved_size_init(void);
 extern void __init hibernate_image_size_init(void);
 
 #ifdef CONFIG_ARCH_HIBERNATION_HEADER
···
 
 #else /* !CONFIG_HIBERNATION */
 
+static inline void hibernate_reserved_size_init(void) {}
 static inline void hibernate_image_size_init(void) {}
 #endif /* !CONFIG_HIBERNATION */
 
···
 
 /* Preferred image size in bytes (default 500 MB) */
 extern unsigned long image_size;
+/* Size of memory reserved for drivers (default SPARE_PAGES x PAGE_SIZE) */
+extern unsigned long reserved_size;
 extern int in_suspend;
 extern dev_t swsusp_resume_device;
 extern sector_t swsusp_resume_block;

kernel/power/snapshot.c

···
 static void swsusp_unset_page_forbidden(struct page *);
 
 /*
+ * Number of bytes to reserve for memory allocations made by device drivers
+ * from their ->freeze() and ->freeze_noirq() callbacks so that they don't
+ * cause image creation to fail (tunable via /sys/power/reserved_size).
+ */
+unsigned long reserved_size;
+
+void __init hibernate_reserved_size_init(void)
+{
+	reserved_size = SPARE_PAGES * PAGE_SIZE;
+}
+
+/*
  * Preferred image size in bytes (tunable via /sys/power/image_size).
  * When it is set to N, the image creating code will do its best to
  * ensure the image size will not exceed N bytes, but if that is
···
  * frame in use.  We also need a number of page frames to be free during
  * hibernation for allocations made while saving the image and for device
  * drivers, in case they need to allocate memory from their hibernation
- * callbacks (these two numbers are given by PAGES_FOR_IO and SPARE_PAGES,
- * respectively, both of which are rough estimates).  To make this happen, we
- * compute the total number of available page frames and allocate at least
+ * callbacks (these two numbers are given by PAGES_FOR_IO (which is a rough
+ * estimate) and reserverd_size divided by PAGE_SIZE (which is tunable through
+ * /sys/power/reserved_size, respectively).  To make this happen, we compute the
+ * total number of available page frames and allocate at least
  *
- * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2 + 2 * SPARE_PAGES
+ * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2
+ *  + 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
  *
  * of them, which corresponds to the maximum size of a hibernation image.
  *
···
 	count -= totalreserve_pages;
 
 	/* Compute the maximum number of saveable pages to leave in memory. */
-	max_size = (count - (size + PAGES_FOR_IO)) / 2 - 2 * SPARE_PAGES;
+	max_size = (count - (size + PAGES_FOR_IO)) / 2
+			- 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE);
 	/* Compute the desired number of image pages specified by image_size. */
 	size = DIV_ROUND_UP(image_size, PAGE_SIZE);
 	if (size > max_size)