On Wed, Jun 22, 2016 at 02:38:22PM +0200, Michal Hocko wrote: > On Wed 22-06-16 11:03:20, Dave Chinner wrote: > > On Tue, Jun 21, 2016 at 04:26:28PM +0200, Michal Hocko wrote: > > > On Wed 15-06-16 17:21:54, Dave Chinner wrote: > [...] > > > > There are allocations outside transaction context which need to be > > > > GFP_NOFS - this is what KM_NOFS was originally intended for. > > > > > > Is it feasible to mark those by the scope NOFS api as well and drop > > > the direct KM_NOFS usage? This should help to identify those that are > > > lockdep only and use the annotation to prevent from the false positives. > > > > I don't understand what you are suggesting here. This all started > > because we use GFP_NOFS in a handful of places to shut up lockdep > > and you didn't want us to use GFP_NOFS like that. Now it sounds to > > me like you are advocating setting unconditional GFP_NOFS allocation > > contexts for entire XFS code paths - whether it's necessary or > > not - to avoid problems with lockdep false positives. > > No, I meant only those paths which need GFP_NOFS for other than lockdep > purposes would use the scope api. > > Anyway, it seems that we are not getting closer to a desired solution > here. Or I am not following it at least... > > It seems that we have effectively two possibilities (from the > MM/lockdep) POV. Either add an explicit API to disable the reclaim > lockdep machinery for all allocation in a certain scope or a GFP mask > to to achieve the same for a particular allocation. Which one would work > better for the xfs usecase? As I've said - if we annotate the XFS call sites appropriately (e.g. KM_NOLOCKDEP rather than KM_NOFS), we don't care what lockdep mechanism is used to turn off warnings as it will be wholly encapsulated inside kmem_alloc() and friends. This will end up similar to how we are currently encapsulate the memalloc_noio_save() wrappers in kmem_zalloc_large(). IOWs, it doesn't matter to XFS whether it be a GFP flag or a PF flag here, because it's not going to be exposed to the higher level code. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>