On Thu 25-06-20 11:48:32, Darrick J. Wong wrote: > On Thu, Jun 25, 2020 at 12:31:16PM +0100, Matthew Wilcox (Oracle) wrote: > > I want a memalloc_nowait like we have memalloc_noio and memalloc_nofs > > for an upcoming patch series, and Jens also wants it for non-blocking > > io_uring. It turns out we already have dm-bufio which could benefit > > from memalloc_nowait, so it may as well go into the tree now. > > > > The biggest problem is that we're basically out of PF_ flags, so we need > > to find somewhere else to store the PF_MEMALLOC_NOWAIT flag. It turns > > out the PF_ flags are really supposed to be used for flags which are > > accessed from other tasks, and the MEMALLOC flags are only going to > > be used by this task. So shuffling everything around frees up some PF > > flags and generally makes the world a better place. > > So, uh, how does this intersect with the patch "xfs: reintroduce > PF_FSTRANS for transaction reservation recursion protection" that > re-adds PF_TRANS because uh I guess we lost some subtlety or another at > some point? This is independent, really. It just relocates the NOFS flag. PF_TRANS is reintroduced for a different reason. When I have replaced the original PF_TRANS by PF_MEMALLOC_NOFS I didn't realized that xfs doesn't need only the NOFS semantic but also the transaction tracking so this cannot be a single bit only. So it has to be added back. But PF_MEMALLOC_NOFS needs to stay for the scoped NOFS semantic. Hope this clarifies it a bit. -- Michal Hocko SUSE Labs
