On (10/10/18 14:29), Dmitry Vyukov wrote: > >> A bit unrelated, but while we are at it: > >> > >> I like it when we rate-limit printk-s that lookup the system. > >> But it seems that default rate-limit values are not always good enough, > >> DEFAULT_RATELIMIT_INTERVAL / DEFAULT_RATELIMIT_BURST can still be too > >> verbose. For instance, when we have a very slow IPMI emulated serial > >> console -- e.g. baud rate at 57600. DEFAULT_RATELIMIT_INTERVAL and > >> DEFAULT_RATELIMIT_BURST can add new OOM headers and backtraces faster > >> than we evict them. > >> > >> Does it sound reasonable enough to use larger than default rate-limits > >> for printk-s in OOM print-outs? OOM reports tend to be somewhat large > >> and the reported numbers are not always *very* unique. > >> > >> What do you think? > > > > I do not really care about the current inerval/burst values. This change > > should be done seprately and ideally with some numbers. > > I think Sergey meant that this place may need to use > larger-than-default values because it prints lots of output per > instance (whereas the default limit is more tuned for cases that print > just 1 line). > > I've found at least 1 place that uses DEFAULT_RATELIMIT_INTERVAL*10: > https://elixir.bootlin.com/linux/latest/source/fs/btrfs/extent-tree.c#L8365 > Probably we need something similar here. Yes, Dmitry, that's what I meant - to use something like DEFAULT_RATELIMIT_INTERVAL * 10 in OOM. I didn't mean to change the default values system wide. --- We are not rate-limiting a single annoying printk() in OOM, but functions that do a whole bunch of printks - OOM header, backtraces, etc. Thus OOM report can be, I don't know, 50 or 70 or 100 lines (who knows). So that's why rate-limit in OOM is more permissive in terms of number of printed lines. When we rate-limit a single printk() we let 10 prinks() /*10 lines*/ max every 5 seconds. While in OOM this transforms into 10 dump_header() + 10 oom_kill_process() every 5 seconds. Still can be too many printk()-s, enough to lockup the system. -ss
