On Tue, 25 Aug 2020 14:34:32 +0900 Joonsoo Kim <js1304@xxxxxxxxx> wrote: > > > > That's a bunch more code on a very hot path to serve an obscure feature > > which has a single obscure callsite. > > > > Can we instead put the burden on that callsite rather than upon > > everyone? For (dumb) example, teach __gup_longterm_locked() to put the > > page back if it's CMA and go get another one? > > Hmm... Unfortunately, it cannot ensure that we eventually get the non-CMA page. > I think that the only way to ensure it is to implement the > functionality here. We can > use 'unlikely' or 'static branch' to reduce the overhead for a really > rare case but > for now I have no idea how to completely remove the overhead. Gee, there must be something? Provide the gup code with a special entry point which takes the page straight from __rmqueue() and bypasses the pcp lists?
