On Wed 18-05-16 11:49:52, Peter Zijlstra wrote: > On Wed, May 18, 2016 at 10:25:39AM +0200, Michal Hocko wrote: > > On Wed 18-05-16 09:20:05, Peter Zijlstra wrote: > > > On Wed, May 18, 2016 at 08:35:49AM +1000, Dave Chinner wrote: > > > > On Tue, May 17, 2016 at 04:49:12PM +0200, Peter Zijlstra wrote: > > [...] > > > > > In any case; would something like this work for you? Its entirely > > > > > untested, but the idea is to mark an entire class to skip reclaim > > > > > validation, instead of marking individual sites. > > > > > > > > Probably would, but it seems like swatting a fly with runaway > > > > train. I'd much prefer a per-site annotation (e.g. as a GFP_ flag) > > > > so that we don't turn off something that will tell us we've made a > > > > mistake while developing new code... > > > > > > Fair enough; if the mm folks don't object to 'wasting' a GFP flag on > > > this the below ought to do I think. > > > > GFP flag space is quite scarse. > > There's still 5 or so bits available, and you could always make gfp_t > u64. It seems we have some places where we encode further data into the same word as gfp_mask (radix tree tags and mapping_flags). From a quick glance they should be OK even with __GFP_BITS_SHIFT increased to 27 but this tells us that we shouldn't consume them without a good reason. > > Especially when it would be used only > > for lockdep configurations which are mostly disabled. Why cannot we go > > with an explicit disable/enable API I have proposed? > > It has unbounded scope. And in that respect the GFP flag thingy is wider > than I'd like too, it avoids setting the state for all held locks, even > though we'd only like to avoid setting it for one class. > > So ideally we'd combine the GFP flag with the previously proposed skip > flag to only avoid marking the one class while keeping everything > working for all other held locks. This is definitely your call but I would prefer starting with something simple and extend it when we find out that the scope/gfp opt-out hides real bugs or it is insufficient for other reasons. I do not this opt out to be used much, quite contrary. We do not hear about false positives reclaim lockdep lockups very often - except for very complex reclaim implementations which are quite uncommon. Thanks! -- Michal Hocko SUSE Labs -- 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>