On Mon, Jul 30, 2018 at 12:36 PM, Rik van Riel <[email protected]> wrote: > On Mon, 2018-07-30 at 12:30 -0700, Andy Lutomirski wrote: >> On Mon, Jul 30, 2018 at 12:15 PM, Rik van Riel <[email protected]> >> wrote: >> > On Mon, 2018-07-30 at 18:26 +0200, Peter Zijlstra wrote: >> > > On Mon, Jul 30, 2018 at 10:30:11AM -0400, Rik van Riel wrote: >> > > >> > > > > What happened to the rework I did there? That not only >> > > > > avoided >> > > > > fiddling >> > > > > with active_mm, but also avoids grab/drop cycles for the >> > > > > other >> > > > > architectures when doing task->kthread->kthread->task things. >> > > > >> > > > I don't think I saw that. I only saw your email from >> > > > July 20th with this fragment of code, which does not >> > > > appear to avoid the grab/drop cycles, and still fiddles >> > > > with active_mm: >> > > >> > > Yeah, that's it. Note how it doesn't do a grab+drop for kernel- >> > > > kernel, >> > > >> > > where the current could would have. >> > > >> > > And also note that it only fiddles with active_mm if it does the >> > > grab+drop thing (the below should have s/ifdef/ifndef/ to make >> > > more >> > > sense maybe). >> > >> > I'll kick off a test with your variant. I don't think we >> > will see any performance difference on x86 (due to not >> > using a refcount at all any more), but unless Ingo is in >> > a hurry I guess there's no issue rewriting this part of >> > the patch series :) >> > >> > Do the other patches look ok to you and Andy? >> > >> >> The whole series other than the active_mm stuff looked okay to me. > > Does the active_mm stuff look like a step in the right > direction with the bugfix, or would you prefer the code > to go in an entirely different direction?
I think it's a big step in the right direction, but it still makes be nervous. I'd be more comfortable with it if you at least had a functional set of patches that result in active_mm being gone, because that will mean that you actually audited the whole mess and fixed anything that might rely on active_mm pointing somewhere or that might be putting a value you didn't take into account into active_mm. IOW I'm not totally thrilled by applying the patches as is if we're still a bit unsure as to what might have gotten missed. I don't think it's at all necessary to redo the patches. Does that seem reasonable? > > If this looks like a step in the right direction, it > may make sense to make this step before the merge window > opens, and continue with more patches in this direction > later. > > -- > All Rights Reversed.
