Hello, Shaohua. On Tue, Aug 29, 2017 at 10:07:04PM -0700, Shaohua Li wrote: > > The association is already coming from the page. We just need to make > > sure that going through loop driver doesn't get in the way of the > > membership getting propagated to the underlying device. > > I think there is confusion. App writes files in upper layer fs on loop. memcg Ah, yes, for some reason, I was still thinking about direct ios. > estabilish membership for the pages of these files. Then writeback does write, > loop then write these pages to under layer fs. The write is done in loop Yes. > thread. The write will allocate new page cache for under layer fs files. The > issue is we must forward memcg info from upper layer files page cache to under > layer files page cache. Ah, I see. We need to assign the ownership of the page cache pages to the original dirtier. Yeah, that's a different problem. For now, let's concentrate on the dio case. > > So, this looks like the loop driver is explicitly forwarding the > > association from the original issuer to the aio command and then from > > the aio command to the ios to the underlying device. I'm wondering > > whether the right way to do this is making aio forward the association > > by default, instead of the loop driver doing it explicitly. That way, > > all aio users can benefit from the forwarding instead of just loop. > > That's possible. The downside doing this in aio is we must audit all fs to make > sure all bio have association. I'd like to avoid doing this if there is no > other loop-like cgroup usage. But wouldn't that mean that we break cgroup membership for aios that users issue? Can't we do this in the generic aio layer? Thanks. -- tejun
