On Thu, Mar 14, 2019 at 5:15 PM Heiner Litz <hlitz@xxxxxxxx> wrote: > > On Thu, Mar 14, 2019 at 7:16 AM Javier González <javier@xxxxxxxxxxx> wrote: > > > > > On 14 Mar 2019, at 06.49, Igor Konopko <igor.j.konopko@xxxxxxxxx> wrote: > > > > > > While reading this patch, idea came to my mind - maybe it would be simply better to get rid of partial read handling from pblk in current form at all and use bio_split() & bio_chain() combination instead? > > > > > > This would definitely reduce a number of this 'kind of complicated' code inside pblk and let block layer help us with that. Even that the performance of such a requests could be a little worse (few smaller IOs instead of single vector IO), I believe that partial read is more a corner case, then a typical use case, so maybe this would be a path to go. > > > > > > Let me know what you think about such an approach - I can make a patch with that if you want. > > I like this idea as it will clean up a lot of code and get rid of the > read_bitmap. > Note that a single request can be turned into up to 32 requests if > cached and non-cached sectors alternate, each one probably requiring > an l2p lookup. I still think it's worth doing though. > When you split, note that you have to release all line_refs which were > acquired during l2p lookup. > > > > > I agree with Igor. > > I agree as well, this path deserves some loving care and cleanup. Let's just try to avoid read tail latency degradation. Simplifying the code is a great first step, then we can optimize if needed be. Thanks for the feedback y'all! > > As I mentioned offline, we should fix this in a way that survives > > further changes in struct bio; either making pblk handling visible to > > the outside or rethinking the whole thing. > > > > Igor: If you can send a patch you mention, it would be great. I have > > been trying the helper approach for some time, but it is too specific, > > as fixing holes in the bvec breaks the bio advance-only semantics. Your > > approach seems much better. > > > > Thanks, > > Javier
