On 21-03-03 14:59:35, Michal Hocko wrote: > On Wed 03-03-21 21:46:44, Feng Tang wrote: > > On Wed, Mar 03, 2021 at 09:18:32PM +0800, Tang, Feng wrote: > > > On Wed, Mar 03, 2021 at 01:32:11PM +0100, Michal Hocko wrote: > > > > On Wed 03-03-21 20:18:33, Feng Tang wrote: > [...] > > > > > One thing I tried which can fix the slowness is: > > > > > > > > > > + gfp_mask &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM); > > > > > > > > > > which explicitly clears the 2 kinds of reclaim. And I thought it's too > > > > > hacky and didn't mention it in the commit log. > > > > > > > > Clearing __GFP_DIRECT_RECLAIM would be the right way to achieve > > > > GFP_NOWAIT semantic. Why would you want to exclude kswapd as well? > > > > > > When I tried gfp_mask &= ~__GFP_DIRECT_RECLAIM, the slowness couldn't > > > be fixed. > > > > I just double checked by rerun the test, 'gfp_mask &= ~__GFP_DIRECT_RECLAIM' > > can also accelerate the allocation much! though is still a little slower than > > this patch. Seems I've messed some of the tries, and sorry for the confusion! > > > > Could this be used as the solution? or the adding another fallback_nodemask way? > > but the latter will change the current API quite a bit. > > I haven't got to the whole series yet. The real question is whether the > first attempt to enforce the preferred mask is a general win. I would > argue that it resembles the existing single node preferred memory policy > because that one doesn't push heavily on the preferred node either. So > dropping just the direct reclaim mode makes some sense to me. > > IIRC this is something I was recommending in an early proposal of the > feature. My assumption [FWIW] is that the usecases we've outlined for multi-preferred would want more heavy pushing on the preference mask. However, maybe the uapi could dictate how hard to try/not try.
