Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755306Ab0K3RQJ (ORCPT ); Tue, 30 Nov 2010 12:16:09 -0500 Received: from gir.skynet.ie ([193.1.99.77]:46836 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755043Ab0K3RPj (ORCPT ); Tue, 30 Nov 2010 12:15:39 -0500 From: Mel Gorman To: Simon Kirby Cc: KOSAKI Motohiro , Shaohua Li , Dave Hansen , linux-mm , linux-kernel , Mel Gorman Subject: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced Date: Tue, 30 Nov 2010 17:15:37 +0000 Message-Id: <1291137339-6323-2-git-send-email-mel@csn.ul.ie> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1291137339-6323-1-git-send-email-mel@csn.ul.ie> References: <1291137339-6323-1-git-send-email-mel@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6759 Lines: 215 When the allocator enters its slow path, kswapd is woken up to balance the node. It continues working until all zones within the node are balanced. For order-0 allocations, this makes perfect sense but for higher orders it can have unintended side-effects. If the zone sizes are imbalanced, kswapd may reclaim heavily on a smaller zone discarding an excessive number of pages. The user-visible behaviour is that kswapd is awake and reclaiming even though plenty of pages are free from a suitable zone. This patch alters the "balance" logic to stop kswapd if any suitable zone becomes balanced to reduce the number of pages it reclaims from other zones. Signed-off-by: Mel Gorman --- include/linux/mmzone.h | 3 ++- mm/page_alloc.c | 2 +- mm/vmscan.c | 48 +++++++++++++++++++++++++++++++++++++++--------- 3 files changed, 42 insertions(+), 11 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 39c24eb..25fe08d 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -645,6 +645,7 @@ typedef struct pglist_data { wait_queue_head_t kswapd_wait; struct task_struct *kswapd; int kswapd_max_order; + enum zone_type high_zoneidx; } pg_data_t; #define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages) @@ -660,7 +661,7 @@ typedef struct pglist_data { extern struct mutex zonelists_mutex; void build_all_zonelists(void *data); -void wakeup_kswapd(struct zone *zone, int order); +void wakeup_kswapd(struct zone *zone, int order, enum zone_type high_zoneidx); int zone_watermark_ok(struct zone *z, int order, unsigned long mark, int classzone_idx, int alloc_flags); enum memmap_context { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 07a6544..344b597 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1921,7 +1921,7 @@ void wake_all_kswapd(unsigned int order, struct zonelist *zonelist, struct zone *zone; for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) - wakeup_kswapd(zone, order); + wakeup_kswapd(zone, order, high_zoneidx); } static inline int diff --git a/mm/vmscan.c b/mm/vmscan.c index d31d7ce..67e4283 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2165,11 +2165,14 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining) * interoperates with the page allocator fallback scheme to ensure that aging * of pages is balanced across the zones. */ -static unsigned long balance_pgdat(pg_data_t *pgdat, int order) +static unsigned long balance_pgdat(pg_data_t *pgdat, int order, + int high_zoneidx) { int all_zones_ok; + int any_zone_ok; int priority; int i; + int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ unsigned long total_scanned; struct reclaim_state *reclaim_state = current->reclaim_state; struct scan_control sc = { @@ -2192,7 +2195,6 @@ loop_again: count_vm_event(PAGEOUTRUN); for (priority = DEF_PRIORITY; priority >= 0; priority--) { - int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ unsigned long lru_pages = 0; int has_under_min_watermark_zone = 0; @@ -2201,6 +2203,7 @@ loop_again: disable_swap_token(); all_zones_ok = 1; + any_zone_ok = 0; /* * Scan in the highmem->dma direction for the highest @@ -2310,10 +2313,12 @@ loop_again: * spectulatively avoid congestion waits */ zone_clear_flag(zone, ZONE_CONGESTED); + if (i <= high_zoneidx) + any_zone_ok = 1; } } - if (all_zones_ok) + if (all_zones_ok || (order && any_zone_ok)) break; /* kswapd: all done */ /* * OK, kswapd is getting into trouble. Take a nap, then take @@ -2336,7 +2341,7 @@ loop_again: break; } out: - if (!all_zones_ok) { + if (!(all_zones_ok || (order && any_zone_ok))) { cond_resched(); try_to_freeze(); @@ -2361,6 +2366,22 @@ out: goto loop_again; } + /* kswapd should always balance all zones for order-0 */ + if (order && !all_zones_ok) { + order = sc.order = 0; + goto loop_again; + } + + /* + * As kswapd could be going to sleep, unconditionally mark all + * zones as uncongested as kswapd is the only mechanism which + * clears congestion flags + */ + for (i = 0; i <= end_zone; i++) { + struct zone *zone = pgdat->node_zones + i; + zone_clear_flag(zone, ZONE_CONGESTED); + } + return sc.nr_reclaimed; } @@ -2380,6 +2401,7 @@ out: static int kswapd(void *p) { unsigned long order; + int zone_highidx; pg_data_t *pgdat = (pg_data_t*)p; struct task_struct *tsk = current; DEFINE_WAIT(wait); @@ -2410,19 +2432,24 @@ static int kswapd(void *p) set_freezable(); order = 0; + zone_highidx = MAX_NR_ZONES; for ( ; ; ) { unsigned long new_order; + int new_zone_highidx; int ret; prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); new_order = pgdat->kswapd_max_order; + new_zone_highidx = pgdat->high_zoneidx; pgdat->kswapd_max_order = 0; - if (order < new_order) { + pgdat->high_zoneidx = MAX_NR_ZONES; + if (order < new_order || new_zone_highidx < zone_highidx) { /* * Don't sleep if someone wants a larger 'order' - * allocation + * allocation or an order at a higher zone */ order = new_order; + zone_highidx = new_zone_highidx; } else { if (!freezing(current) && !kthread_should_stop()) { long remaining = 0; @@ -2451,6 +2478,7 @@ static int kswapd(void *p) } order = pgdat->kswapd_max_order; + zone_highidx = pgdat->high_zoneidx; } finish_wait(&pgdat->kswapd_wait, &wait); @@ -2464,7 +2492,7 @@ static int kswapd(void *p) */ if (!ret) { trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); - balance_pgdat(pgdat, order); + balance_pgdat(pgdat, order, zone_highidx); } } return 0; @@ -2473,7 +2501,7 @@ static int kswapd(void *p) /* * A zone is low on free memory, so wake its kswapd task to service it. */ -void wakeup_kswapd(struct zone *zone, int order) +void wakeup_kswapd(struct zone *zone, int order, enum zone_type high_zoneidx) { pg_data_t *pgdat; @@ -2483,8 +2511,10 @@ void wakeup_kswapd(struct zone *zone, int order) pgdat = zone->zone_pgdat; if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0)) return; - if (pgdat->kswapd_max_order < order) + if (pgdat->kswapd_max_order < order) { pgdat->kswapd_max_order = order; + pgdat->high_zoneidx = min(pgdat->high_zoneidx, high_zoneidx); + } trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) return; -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/