Michal Hocko wrote: > > > > ) rather than by line number, and surround __warn_memalloc_stall() call with > > > > mutex in order to serialize warning messages because it is possible that > > > > multiple allocation requests are stalling? > > > > > > we do not use any lock in warn_alloc_failed so why this should be any > > > different? > > > > warn_alloc_failed() is called for both __GFP_DIRECT_RECLAIM and > > !__GFP_DIRECT_RECLAIM allocation requests, and it is not allowed > > to sleep if !__GFP_DIRECT_RECLAIM. Thus, we have to tolerate that > > concurrent memory allocation failure messages make dmesg output > > unreadable. But __warn_memalloc_stall() is called for only > > __GFP_DIRECT_RECLAIM allocation requests. Thus, we are allowed to > > sleep in order to serialize concurrent memory allocation stall > > messages. > > I still do not see a point. A single line about the warning and locked > dump_stack sounds sufficient to me. printk() is slow operation. It is possible that two allocation requests start within time period needed for completing warn_alloc_failed(). It is possible that multiple concurrent allocations are stalling when one of them cannot be satisfied. The consequence is multiple concurrent timeouts corrupting dmesg. http://I-love.SAKURA.ne.jp/tmp/serial-20160927-nolock.txt.xz (Please ignore Oops at do_task_stat(); it is irrelevant to this topic.) If we guard it with mutex_lock(&oom_lock)/mutex_unlock(&oom_lock), no corruption. http://I-love.SAKURA.ne.jp/tmp/serial-20160927-lock.txt.xz Deferring it when trylock() failed will be also possible. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>