On Fri, 2011-04-22 at 15:35 -0500, Boyd Stephen Smith Jr. wrote: > In <1303435546.3090.3.ca...@zircon.lan.walnut.gen.nz>, Richard Hector > wrote: > >On Wed, 2011-04-20 at 12:04 +0200, Axel Freyn wrote: > >> But the principal problem is: each of those limits/protections > reduces > >> the usability (e.g. if you have 2GB Ram, and you limit eclipse to > 2GB, > >> it will be killed by the Kernel as soon as it tries to use 2GB and > 1 > >> byte from the SWAP > > > >Really? > > > >I'd have thought eclipse's request for more memory (malloc) would > just > >fail at that point - which it may or may not handle appropriately, > and > >may handle by exiting. I see no reason for the kernel to kill it. > > You'd think, right? Since malloc() has nice, documented ways it > fails > gracefully we should use them. > > We do, sometimes. However, in Linux with the default settings, that's > not > entirely true. When over-commit is on, there a minimal checks to see > if a the > memory requested can actually be satisfied. Instead, the map is made > lazily, > when the virtual memory pages are accessed. Unfortunately, it's > possible for > the kernel be unable to satisfy a mapping when it is needed. So, > instead of > failing on "mem = malloc(count)", where the userland process can > handle things > cleanly, the we fail on "*mem = things" were everything has to be > handled in > kernel space. Enter the OOM killer. > > These minimal checks may include what is set by ulimit; I'm not sure.
Yes, I was aware of overcommit (though not the precise details). I guess I assumed that a nice specific requirement like ulimit would be honoured at malloc() time - after all, it's likely to remain fixed, while some other process could free a bunch of memory in time for us to use it - but assumptions are dangerous, of course :-) Thanks, Richard -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/1303526510.2464.3.ca...@zircon.lan.walnut.gen.nz
