Linux & Memory Management (or lack thereof)

Linux & Memory Management (or lack thereof)

Post by Garrett D'Amo » Sat, 08 May 1993 04:52:34



Hello Linuxers,

I encountered an interesting bug (feature?) in Linux recently.  I was
writing some code for a CS class, and I very nearly brough the system
down (Linux system)...

Basically, a piece of my code tried to calloc a big chunk of memory --
279 Mb to be exact!  (I had it output so I could see what was happening.)
But instead of calloc instantly failing and returning a NULL (since I have
only 8 Mb of RAM and 10 Mb of swap), the hard disk started to whir, things
started to slow, and the process hung until I killed it with CTRL-C.  I
thought it was a little optimistic for the kernel to actually try to meet
this request... probably the most obliging kernel I've ever seen... :)

It seems to this poor programmer that the kernel or libraries or whatever,
ought to be smart enough to realize when a request is *clearly* bigger than
any RAM & Virtual RAM available combined, and immediately return a NULL to
the stupid program who asked for such an * amount of memory.  Is this
something that can reasonably be fixed in the next release of the libraries/
kernel, and/or fixed with a patch?

I am running kernel 0.99.pl9, gcc 2.3.3, and shared libs 4.3.3.  I was using
the -Wall -g flags to gcc at the time.

Incidentally, for the curious, I was attempting to implement a one-to-one
bitmapped hash-table.  When I gave it a somewhat unreasonable case, and it
tried to calloc so much space, I decided that a hash table with buckets was
more reasonable to implement.

I can provide source for the code that caused this problem to those debugging
the libraries or kernel.  E-mail me to get a copy.

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