On Mon, Jun 08, 2026 at 04:16:53PM -0400, Gregory Price wrote: > On Mon, Jun 08, 2026 at 03:45:58PM -0400, Michael S. Tsirkin wrote: > > On Mon, Jun 08, 2026 at 11:53:40AM -0400, Gregory Price wrote: > > > > > > If `user_addr` is now implying anything other than exactly: "This needs > > > to be zeroed / caches flushed", then this is bad. > > > > > > ~Gregory > > > > Well if you do folio_zero_user in a non sleepable context then things > > are not going to work. So combining e.g. GFP_ATOMIC and GFP_ZERO and > > user_addr all together is not a good idea. > > > > Can you say whether (GFP_ATOMIC | GFP_ZERO) w/o user_addr has the same > issue?
I don't think it is because it does not call folio_zero_user, right? > If not, then this subtle complexity is now a tripping hazard. Yes. > Is there some combination of arguments here that should just outright > fail if a user attempts it? __GFP_DIRECT_RECLAIM at least. > > > > You are saying it's bad? It's pretty fundamental to the idea of moving > > zeroing into the allocator, I feel. > > > > I'm saying having to infer that safety state from the cobbling of those > things together is not a good pattern (at least as-is). Understood. Don't have a better idea, yet. > If the introduction of user_addr into the mix is the thing that causes > us to have to infer safety, then there's an argument the page allocator > shouldn't handle that operation (in this case: user_addr cache flush). It's not just the flush, we are also trying to use that to optimize zeroing. > > Please consider that this is arguably the most fundamental interface in > in all of mm/. All we're doing is going through the process of figuring > out what changes here are reasonable while trying to meet your goal. > > ~Gregory I don't mind discarding all of this and doing something else completely, but I dislike it that multiple people are apparently now angry that I don't address all the contradictory comments at the same time. I thought just sending a patchset to show how the result looks like is easier than arguing about architecture, and would be helpful. I'm not pushing any of the mm rework, I was asked to do it, myself I just want the ridiculously effective optimization in there. -- MST
