From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, page_alloc: remove redundant checks from alloc fastpath The allocation fast path contains two similar checks for zoneref->zone being NULL, where zoneref points either to the first zone in the zonelist, or to the preferred zone. These can be NULL either due to empty zonelist, or no zone being compatible with given nodemask or task's cpuset. These checks are unnecessary, because the zonelist walks in first_zones_zonelist() and get_page_from_freelist() handle a NULL starting zoneref->zone or preferred_zoneref->zone safely. It's safe to fallback to __alloc_pages_slowpath() where we also have the check early enough. Link: http://lkml.kernel.org/r/20170124150511.5710-1-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 18 ------------------ 1 file changed, 18 deletions(-) diff -puN mm/page_alloc.c~mm-page_alloc-remove-redundant-checks-from-alloc-fastpath mm/page_alloc.c --- a/mm/page_alloc.c~mm-page_alloc-remove-redundant-checks-from-alloc-fastpath +++ a/mm/page_alloc.c @@ -3915,14 +3915,6 @@ static inline bool prepare_alloc_pages(g if (should_fail_alloc_page(gfp_mask, order)) return false; - /* - * Check the zones suitable for the gfp_mask contain at least one - * valid zone. It's possible to have an empty zonelist as a result - * of __GFP_THISNODE and a memoryless node - */ - if (unlikely(!ac->zonelist->_zonerefs->zone)) - return false; - if (IS_ENABLED(CONFIG_CMA) && ac->migratetype == MIGRATE_MOVABLE) *alloc_flags |= ALLOC_CMA; @@ -3962,22 +3954,12 @@ __alloc_pages_nodemask(gfp_t gfp_mask, u return NULL; finalise_ac(gfp_mask, order, &ac); - if (!ac.preferred_zoneref->zone) { - page = NULL; - /* - * This might be due to race with cpuset_current_mems_allowed - * update, so make sure we retry with original nodemask in the - * slow path. - */ - goto no_zone; - } /* First allocation attempt */ page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac); if (likely(page)) goto out; -no_zone: /* * Runtime PM, block IO and its error handling path can deadlock * because I/O on the device might not complete. _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
