>> > I have a program that keeps malloc()ing (and scribbling a bit >> > into the allocated memory) until malloc() fails. The >> > intention is to put pressure on the VM system to find out how >> > much pool cache memory it can reclaim.
>> Such a program would be a prime candidate for declaring itself a >> preferred out-of-swap victim. >> Perhaps even better would be a way for userland to tell the kernel >> "pretend you're under severe RAM pressure and free what you can" >> without needing to actually run the system out of pages. > Is this something madvise(2) could be extended to do? In principle? It could be, sure. I would, however, suggest something else. These operations do not apply to specific ranges of VM, so an API that's designed for actions on particular ranges of VM seems inappropriate. For the former suggestion, for declaring a process a preferred (or maybe even dispreferred) out-of-swap victim, sysctl's proc.$PID.... hierarchy strikes me as a better tool, especially because root can then protect certain processes from the command line, by making them less preferred. I didn't go into details of what I was imagining. I was thinking of each process having a preference; when the kernel runs out of swap, instead of simply killing the faulting process it would kill one of the processes with the maximum victim preference value, perhaps a signed int with the default being zero or some such. Then root could set preference negative for particularly important processes, or positive for fluff, or very positive for things like the "try to reclaim RAM" process outlined. I would say it should be like nice: any process can make itself get less-preferred treatment, but it should take privilege to go the other way. For the latter suggestion, for provoking what reclaims are possible without actually risking running out of pages...I'm not sure. A new syscall? A new sysctl? An ioctl on /dev/mem? There are many possibilities. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
