site_archiver@lists.apple.com Delivered-To: darwin-dev@lists.apple.com Sorry, I was cut off earlier... I suggest filing a problem report. (a) Is malloc() supposed to honor ulimits? Here are my answers, though: Typically these are one user or single purpose machines. -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.appl... On Dec 24, 2008, at 3:05 PM, IainS <developer@sandoe-acoustics.co.uk> wrote: On 24 Dec 2008, at 22:47, Terry Lambert wrote: This can exceed total RAM plus swap because of memory overcommit, which has pretty much been SOP on unix since the DEC VAX version introduced virtual memory. I'm sure you're right --- but these platforms must have had some way of saving you --- I don't remember having this trouble ever on a VAX or a Sun (or even a Prime)... ;-) They mostly did it by having a 32 bit address space, twice as much preconmitted swap as physical RAM. If that didn't work, then thr approach which was commonly used was to kill programs in order to recover resources. A frequent implementation was to pick the first program that asks you for more of any resource for which the request can't be satisfied as a "volunteer". You can also opt a program out of overcommit several ways, but you typically have to replace the malloc, or not use it. Most of these boil down to forcing swap to be preconmitted by dirtying the pages or locking them into physical memory. This is usually inconvenient for both the programmer. Also the other processes sharing the system have to do without those resources, even if they are not being actively used by the greedy precommit process. Subsequent use of the returned pointer can (and does) bring the system down Define "down". unusable - generally to the extent that a hard reboot is required. once you see a "no free paging space left" message thing are looking grim. Yes the system will spend most of its time attempting to clean pages for you to satisfy your applications demands. AFAICT any process that tries to request memory after the system has run out of paging space is put to sleep. Yes, until some can be reclaimed (see above; the alternative is to kill it when it asks). (b) Is malloc() supposed to allow requests in excess of available system resources? Is there any official answer to these? This isn't an official support channel. To get an official answer, you'd need to file a problem report. (a) No. Currently the limits are voluntary. For example, gcc uses getrlimit() to look at the limits and voluntarily limits its working set size by choosing not to exceed the limits. (b) Yes. Allocations that it makes are for virtual, not physical, resources. Virtual resources are effectively near-infinite, and you could be using an algorithm that has sparse utilization of the virtual resources. If so, then there's no reason your algorithm shouldn't be allowed to work, due to an arbitrary administrative limit enforced against a virtual resource. This behavior is troublesome - because a simple non-privileged program compiled -m64 can easily stop the system non-privileged programs ought not to be able to make the system unusable (IMO). Back in my admin days, it was also possible to do this on multiuser machines, and our typical reaction was to disable the offending users account. For a single user machine, you could simply reinstall the offending software and contact the vendor for a fix. does any of the behavior described constitute a bug -- or perhaps an enhancement ? If it cannot be regarded as a bug, perhaps honoring ulimits or providing RLIMIT_VMEM would be a very useful enhancement? You can file a problem report, but we are unlikely to add an RLIMIT_VMEM for the same reason top can't give you an exact answer on who is responsible for shared pages: cardinality hides this information, even from the OS itself. Limiting your processes utilization of the available (by virtue of addressable bits) virtual address space with RLIMIT_DATA is much more likely, but that would be either voluntary or up to its parent process to set before the program is started. This email sent to site_archiver@lists.apple.com