diff options
| -rw-r--r-- | Documentation/power/freezing-of-tasks.txt | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index 04dc1cf9d215..d5c65e8d6a37 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -81,7 +81,16 @@ hibernation image has been created and before the system is finally powered off. 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() callback is executed and it will be 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 |