linux-kernel - Re: [PATCH 1/4] oom: Do not panic when OOM killer is sysrq triggered

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Message-ID: <alpine.DEB.2.10.1507081635030.16585@chino.kir.corp.google.com>
Date:	Wed, 8 Jul 2015 16:36:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jakob Unterwurzacher <jakobunt@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 1/4] oom: Do not panic when OOM killer is sysrq
 triggered

On Wed, 8 Jul 2015, Michal Hocko wrote:

> From: Michal Hocko <mhocko@...e.cz>
> 
> OOM killer might be triggered explicitly via sysrq+f. This is supposed
> to kill a task no matter what e.g. a task is selected even though there
> is an OOM victim on the way to exit. This is a big hammer for an admin
> to help to resolve a memory short condition when the system is not able
> to cope with it on its own in a reasonable time frame (e.g. when the
> system is trashing or the OOM killer cannot make sufficient progress)
> 
> E.g. it doesn't make any sense to obey panic_on_oom setting because
> a) administrator could have used other sysrqs to achieve the
> panic/reboot and b) the policy would break an existing usecase to
> kill a memory hog which would be recoverable unlike the panic which
> might be configured for the real OOM condition.
> 
> It also doesn't make much sense to panic the system when there is no
> OOM killable task because administrator might choose to do additional
> steps before rebooting/panicking the system.
> 
> While we are there also add a comment explaining why
> sysctl_oom_kill_allocating_task doesn't apply to sysrq triggered OOM
> killer even though there is no explicit check and we subtly rely
> on current->mm being NULL for the context from which it is triggered.
> 
> Also be more explicit about sysrq+f behavior in the documentation.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Nack, this is already handled by patch 2 in my series.  I understand that 
the titles were wrong for patches 2 and 3, but it doesn't mean we need to 
add hacks around the code before organizing this into struct oom_control 
or completely pointless comments and printks that will fill the kernel 
log.
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