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SubjectRe: [PATCH v2]mm/oom-kill: direct hardware access processes should get bonus
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> > the victim should not directly access hardware devices like Xorg server,
> > because the hardware could be left in an unpredictable state, although
> > user-application can set /proc/pid/oom_score_adj to protect it. so i think
> > those processes should get 3% bonus for protection.
> >
>
> The logic here is wrong: if killing these tasks can leave hardware in an
> unpredictable state (and that state is presumably harmful), then they
> should be completely immune from oom killing since you're still leaving
> them exposed here to be killed.
>
> So the question that needs to be answered is: why do these threads deserve
> to use 3% more memory (not >4%) than others without getting killed? If
> there was some evidence that these threads have a certain quantity of
> memory they require as a fundamental attribute of CAP_SYS_RAWIO, then I
> have no objection, but that's going to be expressed in a memory quantity
> not a percentage as you have here.

3% is choosed by you :-/


> The CAP_SYS_ADMIN heuristic has a background: it is used in the oom killer
> because we have used the same 3% in __vm_enough_memory() for a long time
> and we want consistency amongst the heuristics. Adding additional bonuses
> with arbitrary values like 3% of memory for things like CAP_SYS_RAWIO
> makes the heuristic less predictable and moves us back toward the old
> heuristic which was almost entirely arbitrary.

That's bogus. __vm_enough_memory() does track virtual adress space. oom-killer
doesn't. It's unrelated.


> Now before KOSAKI-san comes out and says the old heuristic considered
> CAP_SYS_RAWIO and the new one does not so it _must_ be a regression: the
> old heuristic also divided the badness score by 4 for that capability as a
> completely arbitrary value (just like 3% is here). Other traits like
> runtime and nice levels were also removed from the heuristic. What needs
> to be shown is that CAP_SYS_RAWIO requires additional memory just to run
> or we should neglect to free 3% of memory, which could be gigabytes,
> because it has this trait.

Old background is very simple and cleaner.

CAP_SYS_RESOURCE mean the process has a privilege of using more resource.
then, oom-killer gave it additonal bonus.

CAP_SYS_RAWIO mean the process has a direct hardware access privilege
(eg X.org, RDB). and then, killing it might makes system crash.


In another story, somebody doubt 4x bonus is good or not. but 3% has
the same problem.






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