linux-kernel - Re: [PATCH 01/10] perf, tools: Factor out scale conversion code

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Date:   Fri, 14 Oct 2016 09:15:16 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Andi Kleen <andi@...stfloor.org>, jolsa@...nel.org,
        sukadev@...ux.vnet.ibm.com, eranian@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] perf, tools: Factor out scale conversion code

On Fri, Oct 14, 2016 at 01:08:42PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Oct 14, 2016 at 08:45:15AM -0700, Andi Kleen escreveu:
> > > So if we can't convert the scale because of an allocation failure
> > > related to locale issues we silently trow it away and do no scale at
> > > all?
> 
> > That is right. If your machine is thrashing to death in a OOM this
> > is your smallest problem.
> 
> Please keep it was before, i.e. return an error value, and bail out. It
> was like that before, why introduce these kinds of silent "do something
> else in an unlikely case" handling?

Ok. I will fix it.

But just for the record I don't think this fine grained memory error
handling makes any sense for perf. It is needed in the kernel, but
it's not appropiate for user programs:

- Usually when you're out of memory then every thing afterward
that needs memory will fail too, so there's no sane way to continue,
- When you run out of memory in user space you usually get killed
at some point anyways because the OOM killer kicks in.
- The only exception is that you run out of VA space, but then the point
above applies.
- These error paths are all untested and most likely a significant
fraction of them is broken because untested code is often broken.

What most user space does is to just have malloc wrappers that
exit when you run out of memory with an error message. That's nearly
always the right strategy for user programs.

-Andi