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SubjectRe: Some questions about linux kernel.
Date
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Jesse Pollard <pollard@cats-chateau.net> said:

[...]

> It makes it better. The specific process causing the problem is now
> identified.

The only thing you identify this way is the first unsuspecting victim which
happens to step into your trap. The process itself may very well be
innocent, it just finds itself in a position where making a legitimate
request at the wrong moment gets it shot. It depends on all the other stuff
the system is doing at the time: Running NS on an idle, 32Mb machine will
work; if it is also compiling a kernel and rebuilding XFree86 ATM,
something will have to give. Who is at fault? NS isn't, it is doing its
job. Neither are the make, sh, or gcc and whatnot processes doing anything
illegal. Note that all this is completely unrelated to user quotas and
such: User quotas just shift the problem to the individual users, some of
whose innocent processe get killed because of the other things they are
doing. It can be argued that the user is being held responsible this way,
and this is in a sense true. But the process in itself is doing nothing
wrong.

This is one of the reasons why OOM handling is hard: Very often there _is_
no single culprit that can be blamed and clearly deserves to be shot, there
is just a bunch of innocent people some of whom you have to kill or else
all are dead.

You also try to protect the system against malicious (or runaway)
processes. To protect against a runaway memory leak (or dumb mallocbomb)
is rather easy, essentially you shoot the largest/fastest growing process.
Protection against malicious processes is much, much harder, as they _will_
take advantage of blind spots in the detection scheme.

Then there is the fact that this is (or should be, at least for a
well-speced machine) a very rare event, so very little (if any) effort
during normal operation is warranted. This includes the OS and machine, and
even much more importantly the sysadmin.
--
Horst von Brand vonbrand@sleipnir.valparaiso.cl
Casilla 9G, Viña del Mar, Chile +56 32 672616

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