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 <Martin@Lichtvoll.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index 194ca446ac28..b464d12761ba 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -158,3 +158,17 @@ Description:
                 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 <rjw@sisk.pl>
+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.