linux-kernel - Re: [PATCH v1] kernel/trace:check the val against the available mem

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Date:   Wed, 4 Apr 2018 08:23:40 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-patch-test@...ts.linaro.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joel Fernandes <joelaf@...gle.com>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem

On Wed 04-04-18 10:58:39, Zhaoyang Huang wrote:
> On Tue, Apr 3, 2018 at 9:56 PM, Michal Hocko <mhocko@...nel.org> wrote:
> > On Tue 03-04-18 09:32:45, Steven Rostedt wrote:
> >> On Tue, 3 Apr 2018 14:35:14 +0200
> >> Michal Hocko <mhocko@...nel.org> wrote:
> > [...]
> >> > Being clever is OK if it doesn't add a tricky code. And relying on
> >> > si_mem_available is definitely tricky and obscure.
> >>
> >> Can we get the mm subsystem to provide a better method to know if an
> >> allocation will possibly succeed or not before trying it? It doesn't
> >> have to be free of races. Just "if I allocate this many pages right
> >> now, will it work?" If that changes from the time it asks to the time
> >> it allocates, that's fine. I'm not trying to prevent OOM to never
> >> trigger. I just don't want to to trigger consistently.
> >
> > How do you do that without an actuall allocation request? And more
> > fundamentally, what if your _particular_ request is just fine but it
> > will get us so close to the OOM edge that the next legit allocation
> > request simply goes OOM? There is simply no sane interface I can think
> > of that would satisfy a safe/sensible "will it cause OOM" semantic.
> >
> The point is the app which try to allocate the size over the line will escape
> the OOM and let other innocent to be sacrificed. However, the one which you
> mentioned above will be possibly selected by OOM that triggered by consequnce
> failed allocation.

If you are afraid of that then you can have a look at {set,clear}_current_oom_origin()
which will automatically select the current process as an oom victim and
kill it.
-- 
Michal Hocko
SUSE Labs