Re: [PATCH] android,lowmemorykiller: Don't abuse TIF_MEMDIE.

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Mar 08, 2016 at 03:18:59PM +0100, Michal Hocko wrote:
> On Tue 08-03-16 20:01:32, Tetsuo Handa wrote:
> > Currently, lowmemorykiller (LMK) is using TIF_MEMDIE for two purposes.
> > One is to remember processes killed by LMK, and the other is to
> > accelerate termination of processes killed by LMK.
> > 
> > But since LMK is invoked as a memory shrinker function, there still
> > should be some memory available. It is very likely that memory
> > allocations by processes killed by LMK will succeed without using
> > ALLOC_NO_WATERMARKS via TIF_MEMDIE. Even if their allocations cannot
> > escape from memory allocation loop unless they use ALLOC_NO_WATERMARKS,
> > lowmem_deathpending_timeout can guarantee forward progress by choosing
> > next victim process.
> > 
> > On the other hand, mark_oom_victim() assumes that it must be called with
> > oom_lock held and it must not be called after oom_killer_disable() was
> > called. But LMK is calling it without holding oom_lock and checking
> > oom_killer_disabled. It is possible that LMK calls mark_oom_victim()
> > due to allocation requests by kernel threads after current thread
> > returned from oom_killer_disabled(). This will break synchronization
> > for PM/suspend.
> > 
> > This patch introduces per a task_struct flag for remembering processes
> > killed by LMK, and replaces TIF_MEMDIE with that flag. By applying this
> > patch, assumption by mark_oom_victim() becomes true.
> 
> Thanks for looking into this. A separate flag sounds like a better way
> to go (assuming that the flags are not scarce which doesn't seem to be
> the case here).
>  
> The LMK cannot kill the frozen tasks now but this shouldn't be a big deal
> because this is not strictly necessary for the system to move on. We are
> not OOM.
> 
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Michal Hocko <mhocko@suse.cz>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Arve Hjonnevag <arve@android.com>
> > Cc: Riley Andrews <riandrews@android.com>
> 
> Acked-by: Michal Hocko <mhocko@suse.com>

So, any objection for me taking this through the staging tree?

thanks,

greg k-h

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