On 06/01/2016 11:19 AM, Mel Gorman wrote: > On Tue, May 31, 2016 at 11:44:24PM +0200, Vlastimil Babka wrote: >> On 05/30/2016 05:56 PM, Mel Gorman wrote: >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index dba8cfd0b2d6..f2c1e47adc11 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -3232,6 +3232,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int >>> order, >>> * allocations are system rather than user orientated >>> */ >>> ac->zonelist = node_zonelist(numa_node_id(), gfp_mask); >>> + ac->preferred_zoneref = first_zones_zonelist(ac->zonelist, >>> + ac->high_zoneidx, ac->nodemask); >>> + ac->classzone_idx = zonelist_zone_idx(ac->preferred_zoneref); >>> page = get_page_from_freelist(gfp_mask, order, >>> ALLOC_NO_WATERMARKS, ac); >>> if (page) >>> >> >> Even if that didn't help for this report, I think it's needed too >> (except the classzone_idx which doesn't exist anymore?).
But you agree that the hunk above should be merged? >> And I think the following as well. (the changed comment could be also >> just deleted). >> > > Why? > > The comment is fine but I do not see why the recalculation would occur. > > In the original code, the preferred_zoneref for statistics is calculated > based on either the supplied nodemask or cpuset_current_mems_allowed during > the initial attempt. It then relies on the cpuset checks in the slowpath > to encorce mems_allowed but the preferred zone doesn't change. > > With your proposed change, it's possible that the > preferred_zoneref recalculation points to a zoneref disallowed by > cpuset_current_mems_sllowed. While it'll be skipped during allocation, > the statistics will still be against a zone that is potentially outside > what is allowed. Hmm that's true and I was ready to agree. But then I noticed that gfp_to_alloc_flags() can mask out ALLOC_CPUSET for GFP_ATOMIC. So it's like a lighter version of the ALLOC_NO_WATERMARKS situation. In that case it's wrong if we leave ac->preferred_zoneref at a position that has skipped some zones due to mempolicies?
