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SubjectRe: On the issue of low memory situations
Nicholas Vinen wrote:
> Well, you could use SA_RESETHAND with sigaction to specify that
> behaviour but yes, you'd expect that you would almost always want that.
---
Not to belabor the point, but not "almost", but "always".
You wouldn't want it to be under user control -- since
you could end up with non-deterministic or deadlock behavior. This is
one signal that should always reset the action back to 'non-caught'.

> However I do think that such a signal should be triggered before memory is
> TOTALLY exhaused (perhaps if you trigger the allocation of the 5th last
> page in existance or something). This way you have enough pages to do your
> cleanup at least.
---
Dunno if those stats are kept around -- not to mention in a SMP
environment, it wouldn't be that useful -- lez say I have a 16 CPU sys.
My hog processu goes malloc and somehow I determine there are only 5 pages
left. By the time I get that information back to the hog process (it may
get unscheduled), that 5 page figure could have changed N-times, making
it not so useful. One could argue, however, that you could hold 5% of
memory in reserve for UID=0 processes, but what does that mean if we
are running in a capability-based system (where UID=0 means squat) -- I'd
suggest punting that issue to the next rev and deal with the most
pressing matter (I'm outa memory: HELP) more gracefully. I guess we
could add a CAP_USE_LIMITED_MEMORY. When there is x% reserved in an
ext2 filesystem for 'root', which capability does it use? Is there already
a generic CAP_USE_LIMITED_RESOURCES?

> OK, now the only issue is who is going to write this. I'm kinda
> busy this weekend ;) Shouldn't be too hard though. Anyone?
---
Sigh. ;~)
-l
--
Linda A Walsh | Trust Technology, Core Linux, SGI
law@sgi.com | Voice: (650) 933-5338

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