On Fri, May 19, 2017 at 11:31:23AM +0100, Nix wrote: > On 19 May 2017, NeilBrown verbalised: > > > On Wed, May 17 2017, Shaohua Li wrote: > > > >> On Tue, May 16, 2017 at 10:46:13PM +0100, Nix wrote: > >>> Doesn't that already mean that someone has explicitly triggered a check > >>> action? > >> > >> So the idea is: run 'check' and report mismatch, userspace (raid6check for > >> example) uses the reported info to fix the mismatch. The pr_warn_ratelimited > >> isn't a good way to communicate the info to userspace. I'm wondering why we > >> don't just run raid6check solely, it can do the job like what kernel does and > >> we avoid the crappy pr_warn_ratelimited. > > It'll do when there are a few inconsistencies but you don't want to > spend days recovering a huge array to fix a small but nonzero > mismatch_cnt, or to reassure you that yes, these mismatch_cnts are in > swap, ignore them. When there are a lot, enough that a ratelimited > warning hits its rate limit, Neil's right: the array is probably toast. > The limit is then important to stop log flooding. > > > If we really wanted a seamless "fix the raid6 thing" (which I don't > > think we do), > > Oh, I want seamless everything -- the seamlessness and flexibility of md > are its killer features over hardware RAID in my eyes -- but I'm > convinced that this is probably too hard to test and simply too > disruptive to bother with for a likely vanishingly rare failure mode all > entangled with fairly hot paths. > > > we'd probably make the list of inconsistencies appear in a > > sysfs file. That would be less 'crappy'. But as I say, I don't think > > we really want to do that. > > Aren't sysfs files in effect length-limited to one page (or at least > length-limited by virtue of being stored in memory?) It seems to me this > would just bring the same problem ratelimit is solving right back again, > except a sysfs file doesn't have a logging daemon sucking the contents > out constantly so you can overwrite your old output without worrying. > (And there is no other daemon running to do that, except mdadm in > monitor mode, which might not be running and really this job feels out > of scope for it anyway.) No, my question is not the print is ratelimited. The problem is dmesg isn't a good way to communicate info to userspace. You can easily lose all dmesg info with a simple 'dmesg -c'. sysfs file is more reliable. Length-limited isn't a problem, as you said, if there are a lot of mismatch, the array is toast. Alright, I'll accept Neil's suggestion. Unless your guys really need a seamless fix (which I'm still thinking about doing it in usespace by optimizing raid6check) and we'd take this simple warning patch. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
