On Mon, Mar 3, 2025 at 7:56 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 3 Mar 2025 at 08:33, Mateusz Guzik <mjguzik@xxxxxxxxx> wrote: > > > > The stock code already has a dedicated routine to advance the tail, > > adding one for head (instead of an ad-hoc increment) is borderline > > just clean up. > > There's currently a fair number of open-coded assignments: > > git grep -E 'pipe->((tail)|(head)).*=' fs/ > > and some of those are under specific locking rules together with other > updates (ie the watch-queue 'note_loss' thing. > > But hey, if some explicit empty/full flag is simpler, then it > certainly does fit with our current model too, since we already do > have those other flags (exactly like 'note_loss') > > I do particularly hate seeing 'bool' in structures like this. On alpha > it is either fundamentally racy, or it's 32-bit. On other > architectures, it's typically 8 bits for a 1-bit value. > > But we do have holes in that structure where it slots. > I was thinking about just fs/pipe.c. These helpers being used elsewhere is not something I was aware of (or thought would be a thing). The relevant git grep makes me self-nak that patch. :-> But that's some side stuff. Not only it is your call how to proceed, but per the previous e-mail I agree 16-byte head/tail and a 32-byte read would be best. Hopefully the AMD guys will want to take a stab. Otherwise I'll hack it up. -- Mateusz Guzik <mjguzik gmail.com>
