Re: [patch 06/11 -mmotm] oom: move oom_adj value from task_structto mm_struct

[David Rientjes]

On Mon, 11 May 2009, KOSAKI Motohiro wrote:

> 
> > The per-task oom_adj value is a characteristic of its mm more than the
> > task itself since it's not possible to oom kill any thread that shares
> > the mm.  If a task were to be killed while attached to an mm that could
> > not be freed because another thread were set to OOM_DISABLE, it would
> > have needlessly been terminated since there is no potential for future
> > memory freeing.
> > 
> > This patch moves oomkilladj (now more appropriately named oom_adj) from
> > struct task_struct to struct mm_struct.  This requires task_lock() on a
> > task to check its oom_adj value to protect against exec, but it's already
> > necessary to take the lock when dereferencing the mm to find the total VM
> > size for the badness heuristic.
> > 
> > This fixes a livelock if the oom killer chooses a task and another thread
> > sharing the same memory has an oom_adj value of OOM_DISABLE.  This occurs
> > because oom_kill_task() repeatedly returns 1 and refuses to kill the
> > chosen task while select_bad_process() will repeatedly choose the same
> > task during the next retry.
> > 
> > Taking task_lock() in select_bad_process() to check for OOM_DISABLE and
> > in oom_kill_task() to check for threads sharing the same memory will be
> > removed in the next patch in this series where it will no longer be
> > necessary.
> > 
> > Writing to /proc/pid/oom_adj for a kthread will now return -EINVAL since
> > these threads are immune from oom killing already.  They simply report an
> > oom_adj value of OOM_DISABLE.
> 
> David, staging driver shold be standalone.
> Please don't change core kernel for staging.
> 
> if you merge it into mainline, I suggest to you help the driver graduate
> staging.
> 

Umm, all my patches apply fine against mainline since the Android 
lowmemorykiller is already in Linus' tree.  This patch moves oomkilladj 
from struct task_struct to struct mm_struct and since that's used for 
procfs, the oom killer, and the Android lowmemorykiller, I need to modify 
all of them so the kernel will compile with 
CONFIG_ANDROID_LOW_MEMORY_KILLER.
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