On Thu, Nov 17, 2016 at 09:44:39AM +0000, Wols Lists wrote: > On 17/11/16 05:18, NeilBrown wrote: > > On Thu, Nov 17 2016, Shaohua Li wrote: > > > >> Currently raid5-cache update superblock in .quiesce. But since at > >> shutdown/reboot, .quiesce is called with reconfig mutex locked, > >> superblock isn't guaranteed to be called in reclaim thread (see > >> 8e018c21da3). This will make assemble do unnecessary journal recovery. > >> It doesn't corrupt data but is annoying. This adds an extra hook to > >> guarantee journal is flushed to raid disks. And since this hook is > >> called before superblock update, this will guarantee we have a uptodate > >> superblock in shutdown/reboot > > > > Hi. > > I don't quite follow some of the reasoning here. > > In particular, the ->stop_writes() that you have implemented > > does almost exactly the same thing as r5l_quiesce(1). > > So why not simply call ->quiesce(mddev, 1) in __md_stop_writes()?? > > You probably need to also call ->quiesce(mddev, 0) to keep things > > balanced. > > > > Also you have introduced a static mutex (which isn't my favourite sort > > of thing) without giving any explanation why in the changelog comment. > > So I cannot easily see if that addition is at all justified. > > > > Thanks, > > NeilBrown > > > I need to be careful I don't ruffle any feathers here ... > > But this is saying to me this is a nice feature that hasn't been > properly spec'd and thought through. Don't get me wrong, I know that - > in typical linux fashion - people have been adding things, and raid has > "just growed" topsy fashion. So it's incredibly difficult to spec a new > feature when you don't have a spec for the stuff you're building it on. > > Anyways, what I'm saying is, it seems to me this caching stuff (it's a > new feature, iirc) would be great for trying to write out a proper spec > of what's meant to be going on. It'll roll over into spec'ing the stuff > it relies on ... > > And yes, I *AM* volunteering to do the work - as I said elsewhere, I > want to put a load of kerneldoc into the raid source, and get to > understand it all, but the downside is you'll get a lot of newbie-ish > questions from me trying to get to grips with what's going on. I'm an > experienced C programmer but kernel style is alien to me - you know the > disconnect when you're reading something, you can read the words easily, > but you can't decipher the meaning. That's how I feel reading the kernel > source at the moment. > > Are we up for it? Yep, that makes sense. the journal (current write-through mode and upcoming write-back mode) does deserve a description. I'll add something into Documentation dir in kernel source. 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
