On Mon 09-09-19 21:40:24, Tetsuo Handa wrote: > On 2019/09/09 20:36, Michal Hocko wrote: > > On Sat 07-09-19 19:54:32, Tetsuo Handa wrote: > >> (Resending to LKML as linux-mm ML dropped my posts.) > >> > >> If /proc/sys/vm/oom_dump_tasks != 0, dump_header() can become very slow > >> because dump_tasks() synchronously reports all OOM victim candidates, and > >> as a result ratelimit test for dump_header() cannot work as expected. > >> > >> This patch defers dump_tasks() output till oom_lock is released. As a > >> result of this patch, the latency between out_of_memory() is called and > >> SIGKILL is sent (and the OOM reaper starts reclaiming memory) will be > >> significantly reduced. > >> > >> Since CONFIG_PRINTK_CALLER was introduced, concurrent printk() became less > >> problematic. But we still need to correlate synchronously printed messages > >> and asynchronously printed messages if we defer dump_tasks() messages. > >> Thus, this patch also prefixes OOM killer messages using "OOM[$serial]:" > >> format. As a result, OOM killer messages would look like below. > >> > >> [ 31.935015][ T71] OOM[1]: kworker/4:1 invoked oom-killer: gfp_mask=0xcc0(GFP_KERNEL), order=-1, oom_score_adj=0 > >> (...snipped....) > >> [ 32.052635][ T71] OOM[1]: oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),global_oom,task_memcg=/,task=firewalld,pid=737,uid=0 > >> [ 32.056886][ T71] OOM[1]: Out of memory: Killed process 737 (firewalld) total-vm:358672kB, anon-rss:22640kB, file-rss:12328kB, shmem-rss:0kB, UID:0 pgtables:421888kB oom_score_adj:0 > >> [ 32.064291][ T71] OOM[1]: Tasks state (memory values in pages): > >> [ 32.067807][ T71] OOM[1]: [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name > >> [ 32.070057][ T54] oom_reaper: reaped process 737 (firewalld), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB > >> [ 32.072417][ T71] OOM[1]: [ 548] 0 548 9772 1172 110592 0 0 systemd-journal > >> (...snipped....) > >> [ 32.139566][ T71] OOM[1]: [ 737] 0 737 89668 8742 421888 0 0 firewalld > >> (...snipped....) > >> [ 32.221990][ T71] OOM[1]: [ 1300] 48 1300 63025 1788 532480 0 0 httpd > >> > >> This patch might affect panic behavior triggered by panic_on_oom or no > >> OOM-killable tasks, for dump_header(oc, NULL) will not report OOM victim > >> candidates if there are not-yet-reported OOM victim candidates from past > >> rounds of OOM killer invocations. I don't know if that matters. > >> > >> For now this patch embeds "struct oom_task_info" into each > >> "struct task_struct". In order to avoid bloating "struct task_struct", > >> future patch might detach from "struct task_struct" because one > >> "struct oom_task_info" for one "struct signal_struct" will be enough. > > > > This is not an improvement. It detaches the oom report and tasks_dump > > for an arbitrary amount of time because the worder context might be > > stalled for an arbitrary time. Even long after the oom is resolved. > > A new worker thread is created if all existing worker threads are busy > because this patch solves OOM situation quickly when a new worker thread > cannot be created due to OOM situation. > > Also, if a worker thread cannot run due to CPU starvation, the same thing > applies to dump_tasks(). In other words, dump_tasks() cannot complete due > to CPU starvation, which results in more costly and serious consequences. > Being able to send SIGKILL and reclaim memory as soon as possible is > an improvement. There might be zillion workers waiting to make a forward progress and you cannot expect any timing here. Just remember your own experiments with xfs and low memory conditions. > > Not to mention that 1:1 (oom to tasks) information dumping is > > fundamentally broken. Any task might be on an oom list of different > > OOM contexts in different oom scopes (think of OOM happening in disjunct > > NUMA sets). > > I can't understand what you are talking about. This patch just defers > printk() from /proc/sys/vm/oom_dump_tasks != 0. Please look at the patch > carefully. If you are saying that it is bad that OOM victim candidates for > OOM domain B, C, D ... cannot be printed if printing of OOM victim candidates > for OOM domain A has not finished, I can update this patch to print them. You would have to track each ongoing oom context separately. And not only those from different oom scopes because as a matter of fact a new OOM might trigger before the previous dump_tasks managed to be handled. > > This is just adding more kludges and making the code more complex > > without trying to address an underlying problems. So > > Nacked-by: Michal Hocko <mhocko@xxxxxxxx> > > Since I'm sure that you are misunderstanding, this Nacked-by is invalid. Thank you very much for your consideration and evaluation of my review. It seems that I am only burning my time responding to your emails. As you seem to know the best, right? -- Michal Hocko SUSE Labs
