linux-kernel - Re: [PATCH v3 31/35] lib: add memory allocations report in show

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Date: Tue, 20 Feb 2024 18:24:41 +0100
From: Michal Hocko <mhocko@...e.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
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Subject: Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

On Tue 20-02-24 12:18:49, Kent Overstreet wrote:
> On Tue, Feb 20, 2024 at 05:23:29PM +0100, Michal Hocko wrote:
> > On Mon 19-02-24 09:17:36, Suren Baghdasaryan wrote:
> > [...]
> > > For now I think with Vlastimil's __GFP_NOWARN suggestion the code
> > > becomes safe and the only risk is to lose this report. If we get cases
> > > with reports missing this data, we can easily change to reserved
> > > memory.
> > 
> > This is not just about missing part of the oom report. This is annoying
> > but not earth shattering. Eating into very small reserves (that might be
> > the only usable memory while the system is struggling in OOM situation)
> > could cause functional problems that would be non trivial to test for.
> > All that for debugging purposes is just lame. If you want to reuse the code
> > for a different purpose then abstract it and allocate the buffer when you
> > can afford that and use preallocated on when in OOM situation.
> > 
> > We have always went extra mile to avoid potentially disruptive
> > operations from the oom handling code and I do not see any good reason
> > to diverge from that principle.
> 
> Michal, I gave you the logic between dedicated reserves and system
> reserves. Please stop repeating these vague what-ifs.

Your argument makes little sense and it seems that it is impossible to
explain that to you. I gave up on discussing this further with you.

Consider NAK to any additional allocation from oom path unless you can
give very _solid_ arguments this is absolutely necessary. "It's gona be
fine and work most of the time" is not a solid argument.
-- 
Michal Hocko
SUSE Labs