* Michal Hocko <mhocko@xxxxxxxxxx> wrote: > Hi, > > the following patchset implements a killable variant of write lock for > rw_semaphore. My usecase is to turn as many mmap_sem write users to use a > killable variant which will be helpful for the oom_reaper [1] to asynchronously > tear down the oom victim address space which requires mmap_sem for read. This > will reduce a likelihood of OOM livelocks caused by oom victim being stuck on a > lock or other resource which prevents it to reach its exit path and release the > memory. [...] So I'm a tiny bit concerned about this arguments. AFAICS killability here just makes existing system calls more interruptible - right? In that sense that's not really a livelock scenario: it just takes shorter time for resources to be released. If a livelock is possible (where resources are never released) then I'd like to see a specific example of such a livelock. You have the other patch-set: [PATCH 0/18] change mmap_sem taken for write killable that makes use of down_write_killable(), and there you argue: [...] this is a follow up work for oom_reaper [1]. As the async OOM killing depends on oom_sem for read we would really appreciate if a holder for write stood in the way. This patchset is changing many of down_write calls to be killable to help those cases when the writer is blocked and waiting for readers to release the lock and so help __oom_reap_task to process the oom victim. there seems to be a misunderstanding: if a writer is blocked waiting for readers then no new readers are allowed - the writer will get its turn the moment all existing readers drop the lock. So there's no livelock scenario - it's "only" about latencies. And once we realize that it's about latencies (assuming I'm right!), not about correctness per se, I'm wondering whether it would be a good idea to introduce down_write_interruptible(), instead of down_write_killable(). I'd love various processes to quit faster on Ctrl-C as well, not just on kill -9! This would also test the new code paths a lot better: kill -9 is a lot rarer than regular interruption. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
