From: Rafael J. Wysocki <rjw@xxxxxxx> One important reason to freeze tasks, which is that we don't want them to allocate memory after freeing it for the hibernation image, has not been documented. Fix it. Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx> Acked-by: Pavel Machek <pavel@xxxxxx> --- Documentation/power/freezing-of-tasks.txt | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) Index: linux-2.6.22-rc6-mm1/Documentation/power/freezing-of-tasks.txt =================================================================== --- linux-2.6.22-rc6-mm1.orig/Documentation/power/freezing-of-tasks.txt 2007-07-11 20:48:04.000000000 +0200 +++ linux-2.6.22-rc6-mm1/Documentation/power/freezing-of-tasks.txt 2007-07-11 20:50:24.000000000 +0200 @@ -81,7 +81,16 @@ hibernation image has been created and b The majority of these are user space processes, but if any of the kernel threads may cause something like this to happen, they have to be freezable. -2. The second reason is to prevent user space processes and some kernel threads +2. Next, to create the hibernation image we need to free a sufficient amount of +memory (approximately 50% of available RAM) and we need to do that before +devices are deactivated, because we generally need them for swapping out. Then, +after the memory for the image has been freed, we don't want tasks to allocate +additional memory and we prevent them from doing that by freezing them earlier. +[Of course, this also means that device drivers should not allocate substantial +amounts of memory from their .suspend() callbacks before hibernation, but this +is e separate issue.] + +3. The third reason is to prevent user space processes and some kernel threads from interfering with the suspending and resuming of devices. A user space process running on a second CPU while we are suspending devices may, for example, be troublesome and without the freezing of tasks we would need some @@ -111,7 +120,7 @@ frozen before the driver's .suspend() ca thawed after the driver's .resume() callback has run, so it won't be accessing the device while it's suspended. -3. Another reason for freezing tasks is to prevent user space processes from +4. Another reason for freezing tasks is to prevent user space processes from realizing that hibernation (or suspend) operation takes place. Ideally, user space processes should not notice that such a system-wide operation has occurred and should continue running without any problems after the restore (or resume _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
