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Message-ID: <alpine.DEB.2.10.1507091352150.17177@chino.kir.corp.google.com>
Date: Thu, 9 Jul 2015 14:03:53 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Michal Hocko <mhocko@...nel.org>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Jakob Unterwurzacher <jakobunt@...il.com>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] oom: Do not panic when OOM killer is sysrq
triggered
On Thu, 9 Jul 2015, Michal Hocko wrote:
> > 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
>
> It is much easier to backport _fixes_ into older kernels (and yes I do
> care about that) if they do not depend on other cleanups. So I do not
> understand your point here. Besides that the cleanup really didn't make
> much change to the actuall fix because one way or another you still have
> to add a simple condition to rule out a heuristic/configuration which
> doesn't apply to sysrq+f path.
>
> So I am really lost in your argumentation here.
>
This isn't a bugfix: sysrq+f has, at least for eight years, been able to
panic the kernel. We're not fixing a bug, we're changing behavior. It's
quite appropriate to reorganize code before a behavior change to make it
cleaner.
> > or completely pointless comments and printks that will fill the kernel
> > log.
>
> Could you explain what is so pointless about a comment which clarifies
> the fact which is not obviously visible from the current function?
>
It states the obvious, a kthread is not going to be oom killed for
oom_kill_allocating_task: it's not only current->mm, but also
oom_unkillable_task(), which quite explicitly checks for PF_KTHREAD. I
don't think any reader of this code will assume a kthread is going to be
oom killed.
> Also could you explain why the admin shouldn't get an information if
> sysrq+f didn't kill anything because no eligible task has been found?
The kernel log is the only notification mechanism that we have of the
kernel killing a process, we want to avoid spamming it unnecessarily. The
kernel log is not the appropriate place for your debugging information
that would only specify that yes, out_of_memory() was called, but there
was nothing actionable, especially when that trigger can be constantly
invoked by userspace once panicking is no longer possible.
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