What to do when out of memory

[Ed McCaul]

Again, I do not know who put me on this list but I do not want to be on it.






At 11:43 AM 1/24/00 +0000, John Ripley wrote:
>Andreas Bombe wrote:
> >
> > On Sat, Jan 22, 2000 at 04:13:33AM +0000, Aaron Lehmann wrote:
> > > The basic problem is that if I run a program that eats up all the memory
> > > on the system than the kernel will start swapping crazilly and make the
> > > system completely unresponsive.
> > [...]
> > > I know that your first impulse will be to tell me to set PAM's 
> limits.conf
> > > or a limits option within my shell. I think this is irrelevant. 
> Regardless
> > > of userspace settings, the kernel should handle OOM situations more
> > > gracefully than swapping to death. This may be a gross oversimplification
> > > of the problem (as I have no kernel hacking experience or knowledge), but
> > > can't the kernel just deny memory allocations if all the memory on the
> > > system is in use?
> >
> > 2.2 and later don't allocate more memory to user space than is
> > available unless overcommit_memory is explicitly set.  And if you don't
> > want the kernel to swap when memory gets tight then don't add a swap
> > partition/file in the first place, easy.
>
>Actually, Linux will allow to you allocate almost infinite amounts of
>memory, so long as you only allocate it in chunks smaller than
>physical+swap:
>
>- If you're on a machine with swap, when you get round to using it (or
>use mlockall) things swap like mad and eventually block (or hard lock,
>which my 2.3.39 machine does).
>
>- On a machine without swap, when you get round to using it, it'll
>SIGBUS. Or another random process that schedules will SIGBUS as its
>libraries or executable gets page faulted, and can't page.
>
>In neither case did mmap or brk return ENOMEM. The only notification the
>process got of running out of memory was being killed.
>
>It seems it is possible to keep track of memory such that any successful
>mmap will always be pageable - keep track of allocated pages which are
>pending paging and subtract that from free_pages in vm_enough_memory().
>Still, this is getting back to a short thread I started long ago - if I
>have some spare time I'll try implementing it.
>
>--
>John Ripley, empeg Ltd.
>http://www.empeg.com
>
>-
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