On Fri 18-04-14 13:06:38, Andrew Morton wrote:
> From: Mel Gorman <mgorman@xxxxxxx>
> Subject: mm: page_alloc: do not cache reclaim distances
>
> pgdat->reclaim_nodes tracks if a remote node is allowed to be reclaimed by
> zone_reclaim due to its distance. As it is expected that zone_reclaim_mode
> will be rarely enabled it is unreasonable for all machines to take a penalty.
> Fortunately, the zone_reclaim_mode() path is already slow and it is the path
> that takes the hit.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> include/linux/mmzone.h | 1 -
> mm/page_alloc.c | 15 ++-------------
> 2 files changed, 2 insertions(+), 14 deletions(-)
>
> diff -puN include/linux/mmzone.h~mm-page_alloc-do-not-cache-reclaim-distances include/linux/mmzone.h
> --- a/include/linux/mmzone.h~mm-page_alloc-do-not-cache-reclaim-distances
> +++ a/include/linux/mmzone.h
> @@ -763,7 +763,6 @@ typedef struct pglist_data {
> unsigned long node_spanned_pages; /* total size of physical page
> range, including holes */
> int node_id;
> - nodemask_t reclaim_nodes; /* Nodes allowed to reclaim from */
> wait_queue_head_t kswapd_wait;
> wait_queue_head_t pfmemalloc_wait;
> struct task_struct *kswapd; /* Protected by lock_memory_hotplug() */
> diff -puN mm/page_alloc.c~mm-page_alloc-do-not-cache-reclaim-distances mm/page_alloc.c
> --- a/mm/page_alloc.c~mm-page_alloc-do-not-cache-reclaim-distances
> +++ a/mm/page_alloc.c
> @@ -1850,16 +1850,8 @@ static bool zone_local(struct zone *loca
>
> static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
> {
> - return node_isset(local_zone->node, zone->zone_pgdat->reclaim_nodes);
> -}
> -
> -static void __paginginit init_zone_allows_reclaim(int nid)
> -{
> - int i;
> -
> - for_each_node_state(i, N_MEMORY)
> - if (node_distance(nid, i) <= RECLAIM_DISTANCE)
> - node_set(i, NODE_DATA(nid)->reclaim_nodes);
> + return node_distance(zone_to_nid(local_zone), zone_to_nid(zone)) <
> + RECLAIM_DISTANCE;
It is not clear to me why we do not have to care about memory less
nodes in zone_allows_reclaim anymore. Those were excluded during the
initialization previously but we can consider them now if they are in
the zonelist. I have seen such memoryless nodes only on ppc and the
distance was > RECLAIM_DISTANCE so it is probably not a problem, but who
knows what will come later and a comment wouldn't hurt.
> }
>
> #else /* CONFIG_NUMA */
> @@ -1893,9 +1885,6 @@ static bool zone_allows_reclaim(struct z
> return true;
> }
>
> -static inline void init_zone_allows_reclaim(int nid)
> -{
> -}
> #endif /* CONFIG_NUMA */
>
> /*
--
Michal Hocko
SUSE Labs
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