If you have two default tmpfs instances on your box (hi buildroot!) and they're world writeable and a normal user goes "cat /dev/zero > /run/fillit; cat /dev/zero > /tmp/fillit" the system then goes "sh: can't fork" trying to call rm on those files, because they each default to 50% of total system memory, no matter how many instances there are. It only stops writing when memory allocation fails in the kernel.
I'm not quite sure how to fix that. I want to say "change the default to be 50% of what's _left_" (and if you size= manually you get to keep the pieces) but define "what's left"? Other things are using some memory already, the 50% _was_ the amount it's safe for tmpfs to use. (Once upon a time the logic was that 50% of memory can go to disk cache. I think that's gotten a bit more complicated since then? No idea what the current rules are.) This is related to the guy who wanted initramfs to be ramfs instead of tmpfs because he had a cpio.gz that extracted to >50% of system memory so it extracted fine with ramfs but hit the limit and failed with tmpfs. That sounds like a tmpfs rootfs (I.E. initmpfs) should start with a limit of 90% and then scale it _down_ to 50% after extracting the cpio. (I wonder what happens if you -o remount the size= limit to smaller than the filesystem currently holds? Hmmm...) Rob P.S. Yes I need to pipe rootflags= through so you can specify the size on the command line. I've got 3 or 4 initramfs/tmpfs plates spinning and haven't had a chance to work on them all merge window. I'll try to get some patches ready by next weekend, if they miss the release they miss the release...
