On Mon, 21 Jun 2010 18:23:03 -0700 (PDT) Roland McGrath <roland@xxxxxxxxxx> wrote: > A core dump is just an instance of a process suddenly reading lots of its > address space and doing lots of filesystem writes, producing the kinds of > thrashing that any such instance might entail. It really seems like the > real solution to this kind of problem will be in some more general kind of > throttling of processes (or whatever manner of collections thereof) when > they got hog-wild on page-ins or filesystem writes, or whatever else. I'm > not trying to get into the details of what that would be. But I have to > cite this hack as the off-topic kludge that it really is. That said, I do > certainly sympathize with the desire for a quick hack that addresses the > scenario you experience. yup. > For the case you described, it seems to me that constraining concurrency > per se would be better than punting core dumps when too concurrent. That > is, you should not skip the dump when you hit the limit. Rather, you > should block in do_coredump() until the next dump already in progress > finishes. (It should be possible to use TASK_KILLABLE so that those dumps > in waiting can be aborted with a follow-on SIGKILL. But Oleg will have to > check on the signals details being right for that.) yup. Might be able to use semaphores for this. Use sema_init(), down_killable() and up(). Modifying the max concurrency value would require a loop of up()s and down()s, probably all surrounded by a mutex_lock. Which is a bit ugly, and should be done in kernel/semaphore.c I guess. > That won't make your crashers each complete quickly, but it will prevent > the thrashing. Instead of some crashers suddenly not producing dumps at > all, they'll just all queue up waiting to finish crashing but not using any > CPU or IO resources. That way you don't lose any core dumps unless you > want to start SIGKILL'ing things (which oom_kill might do if need be), > you just don't die in flames trying to do nothing but dump cores. A global knob is a bit old-school. Perhaps it should be a per-memcg knob or something. otoh, one could perhaps toss all these tasks into a blkio_cgroup and solve this problem with the block IO controller. After all, that's what it's for. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
