On 7/13/20 2:17 AM, Pavel Begunkov wrote: > On 12/07/2020 23:32, Jens Axboe wrote: >> On 7/12/20 11:34 AM, Pavel Begunkov wrote: >>> On 12/07/2020 18:59, Jens Axboe wrote: >>>> On 7/12/20 3:41 AM, Pavel Begunkov wrote: >>>>> Make io_kiocb slimmer by 24 bytes mainly by revising lists usage. The >>>>> drawback is adding extra kmalloc in draining path, but that's a slow >>>>> path, so meh. It also frees some space for the deferred completion path >>>>> if would be needed in the future, but the main idea here is to shrink it >>>>> to 3 cachelines in the end. >>>>> >>>>> I'm not happy yet with a few details, so that's not final, but it would >>>>> be lovely to hear some feedback. >>>> >>>> I think it looks pretty good, most of the changes are straight forward. >>>> Adding a completion entry that shares the submit space is a good idea, >>>> and really helps bring it together. >>>> >>>> From a quick look, the only part I'm not super crazy about is patch #3. >>> >>> Thanks! >>> >>>> I'd probably rather use a generic list name and not unionize the tw >>>> lists. >>> >>> I don't care much, but without compiler's help always have troubles >>> finding and distinguishing something as generic as "list". >> >> To me, it's easier to verify that we're doing the right thing when they >> use the same list member. Otherwise you have to cross reference two >> different names, easier to shoot yourself in the foot that way. So I'd >> prefer just retaining it as 'list' or something generic. > > If you don't have objections, I'll just leave it "inflight_entry". This > one is easy to grep. Sure, don't have strong feelings on the actual name. >>> BTW, I thought out how to bring it down to 3 cache lines, but that would >>> require taking io_wq_work out of io_kiocb and kmalloc'ing it on demand. >>> And there should also be a bunch of nice side effects like improving apoll. >> >> How would this work with the current use of io_wq_work as storage for >> whatever bits we're hanging on to? I guess it could work with a prep >> series first more cleanly separating it, though I do feel like we've >> been getting closer to that already. > > It's definitely not a single patch. I'm going to prepare a series for > discussion later, and then we'll see whether it worth it. Definitely not. Let's flesh this one out first, then we can move on. -- Jens Axboe
