On 06/19/2018 06:24 PM, Dan Williams wrote: > On Tue, Jun 19, 2018 at 11:11 AM, John Hubbard <jhubbard@xxxxxxxxxx> wrote: >> On 06/19/2018 03:41 AM, Jan Kara wrote: >>> On Tue 19-06-18 02:02:55, Matthew Wilcox wrote: >>>> On Tue, Jun 19, 2018 at 10:29:49AM +0200, Jan Kara wrote: > [..] >>> And then there's the aspect that both these approaches are a bit too >>> heavyweight for some get_user_pages_fast() users (e.g. direct IO) - Al Viro >>> had an idea to use page lock for that path but e.g. fs/direct-io.c would have >>> problems due to lock ordering constraints (filesystem ->get_block would >>> suddently get called with the page lock held). But we can probably leave >>> performance optimizations for phase two. >> >> >> So I assume that phase one would be to apply this approach only to >> get_user_pages_longterm. (Please let me know if that's wrong.) > > I think that's wrong, because get_user_pages_longterm() is only a > filesystem-dax avoidance mechanism, it's not trying to address all the > problems that Jan is talking about. I don't see any viable half-step > solutions. > OK, but in that case, I'm slightly confused by Jan's comment above, about leaving performance optimizations until phase two. Because that *is* a half-step approach: phase one, phase two. Are you disagreeing with Jan, or are you suggesting "fix get_user_pages first, and leave get_user_pages_fast alone for now?" Or something else?
