On Wed 03-10-18 17:07:13, Anshuman Khandual wrote: > > > On 10/03/2018 04:29 PM, Michal Hocko wrote: [...] > > It is not the platform that decides. That is the whole point of the > > distinction. It is us to say what is feasible and what we want to > > support. Do we want to support giga pages in zone_movable? Under which > > conditions? See my point? > > So huge_movable() is going to be a generic MM function deciding on the > feasibility for allocating a huge page of 'size' from movable zone during > migration. Yeah, this might be a more complex logic than just the size check. If there is a sufficient pre-allocated pool to migrate the page off it might be pre-reserved for future migration etc... Nothing to be done right now of course. > If the feasibility turns out to be negative, then migration > process is aborted there. You are still confusing allocation and migration here I am afraid. The whole "feasible to migrate" is for the _allocation_ time when we decide whether the new page should be placed in zone_movable or not. > huge_movable() will do something like these: > > - Return positive right away on smaller size huge pages > - Measure movable allocation feasibility for bigger huge pages > - Look out for free_pages in the huge page order in movable areas > - if (order > (MAX_ORDER - 1)) > - Scan the PFN ranges in movable zone for possible allocation > - etc > - etc > > Did I get this right ? Well, not really. I was thinking of something like this for the beginning if (!arch_hugepage_migration_supporte()) return false; if (hstate_is_gigantic(h)) return false; return true; further changes might be done on top of this. -- Michal Hocko SUSE Labs
