Re: [PATCH 3/6] mm, PM/Freezer: Disable OOM killer when tasks are frozen

[Pavel Machek <pavel@ucw.cz>]

On Wed 2009-05-13 10:37:49, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@sisk.pl>
> 
> Currently, the following scenario appears to be possible in theory:
> 
> * Tasks are frozen for hibernation or suspend.
> * Free pages are almost exhausted.
> * Certain piece of code in the suspend code path attempts to allocate
>   some memory using GFP_KERNEL and allocation order less than or
>   equal to PAGE_ALLOC_COSTLY_ORDER.
> * __alloc_pages_internal() cannot find a free page so it invokes the
>   OOM killer.
> * The OOM killer attempts to kill a task, but the task is frozen, so
>   it doesn't die immediately.
> * __alloc_pages_internal() jumps to 'restart', unsuccessfully tries
>   to find a free page and invokes the OOM killer.
> * No progress can be made.
> 
> Although it is now hard to trigger during hibernation due to the
> memory shrinking carried out by the hibernation code, it is
> theoretically possible to trigger during suspend after the memory
> shrinking has been removed from that code path.  Moreover, since
> memory allocations are going to be used for the hibernation memory
> shrinking, it will be even more likely to happen during hibernation.
> 
> To prevent it from happening, introduce the oom_killer_disabled
> switch that will cause __alloc_pages_internal() to fail in the
> situations in which the OOM killer would have been called and make
> the freezer set this switch after tasks have been successfully
> frozen.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Acked-by: Pavel Machek <pavel@ucw.cz>

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