On Thu, 28 Jul 2016, Michal Hocko wrote: > > >> I think we'd end up with cleaner code if we removed the cute-hacks. And > > >> we'd be able to use 6 more GFP flags!! (though I do wonder if we really > > >> need all those 26). > > > > > > Well, maybe we are able to remove those hacks, I wouldn't definitely > > > be opposed. But right now I am not even convinced that the mempool > > > specific gfp flags is the right way to go. > > > > I'm not suggesting a mempool-specific gfp flag. I'm suggesting a > > transient-allocation gfp flag, which would be quite useful for mempool. > > > > Can you give more details on why using a gfp flag isn't your first choice > > for guiding what happens when the system is trying to get a free page > > :-? > > If we get rid of throttle_vm_writeout then I guess it might turn out to > be unnecessary. There are other places which will still throttle but I > believe those should be kept regardless of who is doing the allocation > because they are helping the LRU scanning sane. I might be wrong here > and bailing out from the reclaim rather than waiting would turn out > better for some users but I would like to see whether the first approach > works reasonably well. If we are swapping to a dm-crypt device, the dm-crypt device is congested and the underlying block device is not congested, we should not throttle mempool allocations made from the dm-crypt workqueue. Not even a little bit. So, I think, mempool_alloc should set PF_NO_THROTTLE (or __GFP_NO_THROTTLE). Mikulas > -- > Michal Hocko > SUSE Labs > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
