From: Oscar Salvador <osalvador@xxxxxxx> Subject: mm/page_alloc.c: clean up check_for_memory() check_for_memory() looks a bit confusing. First of all, we have this: if (N_MEMORY == N_NORMAL_MEMORY) return; Checking the ENUM declaration, looks like N_MEMORY canot be equal to N_NORMAL_MEMORY. I could not find where N_MEMORY is set to N_NORMAL_MEMORY, or the other way around either, so unless I am missing something, this condition will never evaluate to true. It makes sense to get rid of it. Moving forward, the operations within the loop look a bit confusing as well. We set N_HIGH_MEMORY unconditionally, and then we set N_NORMAL_MEMORY in case we have CONFIG_HIGHMEM (N_NORMAL_MEMORY != N_HIGH_MEMORY) and zone <= ZONE_NORMAL. (N_HIGH_MEMORY falls back to N_NORMAL_MEMORY on !CONFIG_HIGHMEM systems, and that is why we can just go ahead and set N_HIGH_MEMORY unconditionally) Although this works, it is a bit subtle. I think that this could be easier to follow: First, we should only set N_HIGH_MEMORY in case we have CONFIG_HIGHMEM. And then we should set N_NORMAL_MEMORY in case zone <= ZONE_NORMAL, without further checking whether we have CONFIG_HIGHMEM or not. Link: http://lkml.kernel.org/r/20180828210158.4617-1-osalvador@xxxxxxxxxxxxxxxxxx Signed-off-by: Oscar Salvador <osalvador@xxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Michael Hocko <mhocko@xxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) --- a/mm/page_alloc.c~mm-page_alloc-clean-up-check_for_memory +++ a/mm/page_alloc.c @@ -6803,15 +6803,12 @@ static void check_for_memory(pg_data_t * { enum zone_type zone_type; - if (N_MEMORY == N_NORMAL_MEMORY) - return; - for (zone_type = 0; zone_type <= ZONE_MOVABLE - 1; zone_type++) { struct zone *zone = &pgdat->node_zones[zone_type]; if (populated_zone(zone)) { - node_set_state(nid, N_HIGH_MEMORY); - if (N_NORMAL_MEMORY != N_HIGH_MEMORY && - zone_type <= ZONE_NORMAL) + if (IS_ENABLED(CONFIG_HIGHMEM)) + node_set_state(nid, N_HIGH_MEMORY); + if (zone_type <= ZONE_NORMAL) node_set_state(nid, N_NORMAL_MEMORY); break; } _
