On Mon, 11 Mar 2024 09:37:36 +0800 "Huang, Ying" <ying.huang@xxxxxxxxx> wrote: > > @@ -2515,15 +2516,26 @@ int mpol_misplaced(struct folio *folio, struct vm_fault *vmf, > > break; > > > > case MPOL_BIND: > > - /* Optimize placement among multiple nodes via NUMA balancing */ > > + case MPOL_PREFERRED_MANY: > > + /* > > + * Even though MPOL_PREFERRED_MANY can allocate pages outside > > + * policy nodemask we don't allow numa migration to nodes > > + * outside policy nodemask for now. This is done so that if we > > + * want demotion to slow memory to happen, before allocating > > + * from some DRAM node say 'x', we will end up using a > > + * MPOL_PREFERRED_MANY mask excluding node 'x'. In such scenario > > + * we should not promote to node 'x' from slow memory node. > > + */ > > This is a little hard to digest for me. And, I don't think that we need > to put this policy choice in code comments. It's better to put it in > patch description. Where we can give more background, for example, to > avoid cross-socket traffic, etc. Oh. I like the comment. We could perhaps put additional detail in the changelog, but using changelogs to understand the code is so darned inconvenient.
