linux-kernel - Re: [PATCH v5] mm: Add memory allocation watchdog kernel thread.

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Date:	Fri, 13 May 2016 00:09:07 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	hillf.zj@...baba-inc.com, mhocko@...nel.org
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5] mm: Add memory allocation watchdog kernel thread.

Hillf Danton wrote:
> > +struct memalloc_info {
> > +	/*
> > +	 * 0: not doing __GFP_RECLAIM allocation.
> > +	 * 1: doing non-recursive __GFP_RECLAIM allocation.
> > +	 * 2: doing recursive __GFP_RECLAIM allocation.
> > +	 */
> > +	u8 valid;
> > +	/*
> > +	 * bit 0: Will be reported as OOM victim.
> > +	 * bit 1: Will be reported as dying task.
> > +	 * bit 2: Will be reported as stalling task.
> > +	 * bit 3: Will be reported as exiting task.
> > +	 * bit 7: Will be reported unconditionally.
> > +	 */
> > +	u8 type;
> > +	/* Index used for memalloc_in_flight[] counter. */
> > +	u8 idx;
> 
> 	u8 __pad;	is also needed perhaps.
> 

Since this structure is not marked as __packed, I think that
the compiler will automatically pad it.

> The numbers assigned to type may be replaced with texts, 
> for instance,
> 	MEMALLOC_TYPE_VICTIM 
> 	MEMALLOC_TYPE_DYING 
> 	MEMALLOC_TYPE_STALLING
> 	MEMALLOC_TYPE_EXITING
> 	MEMALLOC_TYPE_REPORT
> 

I can define them as bit shift numbers. Thanks.

Michal, this version eliminated overhead of walking the process list
when nothing is wrong. You are aware of the possibility of
debug_show_all_locks() failing to report the culprit, aren't you?
So, what are unacceptable major problems for you?