Michal Hocko wrote: > On Thu 09-11-17 19:22:58, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > Hi, > > > assuming that this passes warn stall torturing by Tetsuo, do you think > > > we can drop > > > http://lkml.kernel.org/r/1509017339-4802-1-git-send-email-penguin-ker...@i-love.sakura.ne.jp > > > from the mmotm tree? > > > > I don't think so. > > > > The rule that "do not try to printk() faster than the kernel can write to > > consoles" will remain no matter how printk() changes. Unless asynchronous > > approach like https://lwn.net/Articles/723447/ is used, I think we can't > > obtain useful information. > > Does that mean that the patch doesn't pass your test? >
Test is irrelevant. See the changelog. Synchronous approach is prone to unexpected results (e.g. too late [1], too frequent [2], overlooked [3]). As far as I know, warn_alloc() never helped with providing information other than "something is going wrong". I want to consider asynchronous approach which can obtain information during stalls with possibly relevant threads (e.g. the owner of oom_lock and kswapd-like threads) and serve as a trigger for actions (e.g. turn on/off tracepoints, ask libvirt daemon to take a memory dump of stalling KVM guest for diagnostic purpose). [1] https://bugzilla.kernel.org/show_bug.cgi?id=192981 [2] http://lkml.kernel.org/r/cam_iqpwupvgc2ky8m-9yukects+zkjidasnymx7rmcbjbfy...@mail.gmail.com [3] commit db73ee0d46379922 ("mm, vmscan: do not loop on too_many_isolated for ever")
