Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1435593 > unrolled thread

[PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 22:10 +0200
    Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-07 03:10 +0200
      Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-07 11:50 +0200
        Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-08 04:30 +0200
          Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-08 12:10 +0200

#1435593 — [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

This patch makes reclaim decisions on a per-node basis.  A reclaimer knows
what zone is required by the allocation request and skips pages from
higher zones.  In many cases this will be ok because it's a GFP_HIGHMEM
request of some description.  On 64-bit, ZONE_DMA32 requests will cause
some problems but 32-bit devices on 64-bit platforms are increasingly
rare.  Historically it would have been a major problem on 32-bit with big
Highmem:Lowmem ratios but such configurations are also now rare and even
where they exist, they are not encouraged.  If it really becomes a
problem, it'll manifest as very low reclaim efficiencies.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/vmscan.c | 79 ++++++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 55 insertions(+), 24 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 86a523a761c9..766b36bec829 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -84,6 +84,9 @@ struct scan_control {
 	/* Scan (total_size >> priority) pages at once */
 	int priority;
 
+	/* The highest zone to isolate pages for reclaim from */
+	enum zone_type reclaim_idx;
+
 	unsigned int may_writepage:1;
 
 	/* Can mapped pages be reclaimed? */
@@ -1392,6 +1395,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	unsigned long nr_taken = 0;
 	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
 	unsigned long scan, nr_pages;
+	LIST_HEAD(pages_skipped);
 
 	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
 					!list_empty(src); scan++) {
@@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 
 		VM_BUG_ON_PAGE(!PageLRU(page), page);
 
+		if (page_zonenum(page) > sc->reclaim_idx) {
+			list_move(&page->lru, &pages_skipped);
+			continue;
+		}
+
 		switch (__isolate_lru_page(page, mode)) {
 		case 0:
 			nr_pages = hpage_nr_pages(page);
@@ -1420,6 +1429,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		}
 	}
 
+	/*
+	 * Splice any skipped pages to the start of the LRU list. Note that
+	 * this disrupts the LRU order when reclaiming for lower zones but
+	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
+	 * scanning would soon rescan the same pages to skip and put the
+	 * system at risk of premature OOM.
+	 */
+	if (!list_empty(&pages_skipped))
+		list_splice(&pages_skipped, src);
 	*nr_scanned = scan;
 	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
 				    nr_taken, mode, is_file_lru(lru));
@@ -1589,7 +1607,7 @@ static int current_may_throttle(void)
 }
 
 /*
- * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
+ * shrink_inactive_list() is a helper for shrink_node().  It returns the number
  * of reclaimed pages
  */
 static noinline_for_stack unsigned long
@@ -2401,12 +2419,13 @@ static inline bool should_continue_reclaim(struct zone *zone,
 	}
 }
 
-static bool shrink_zone(struct zone *zone, struct scan_control *sc,
-			bool is_classzone)
+static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc,
+			enum zone_type classzone_idx)
 {
 	struct reclaim_state *reclaim_state = current->reclaim_state;
 	unsigned long nr_reclaimed, nr_scanned;
 	bool reclaimable = false;
+	struct zone *zone = &pgdat->node_zones[classzone_idx];
 
 	do {
 		struct mem_cgroup *root = sc->target_mem_cgroup;
@@ -2438,7 +2457,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
 			shrink_zone_memcg(zone, memcg, sc, &lru_pages);
 			zone_lru_pages += lru_pages;
 
-			if (memcg && is_classzone)
+			if (!global_reclaim(sc))
 				shrink_slab(sc->gfp_mask, zone_to_nid(zone),
 					    memcg, sc->nr_scanned - scanned,
 					    lru_pages);
@@ -2469,7 +2488,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
 		 * Shrink the slab caches in the same proportion that
 		 * the eligible LRU pages were scanned.
 		 */
-		if (global_reclaim(sc) && is_classzone)
+		if (global_reclaim(sc))
 			shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
 				    sc->nr_scanned - nr_scanned,
 				    zone_lru_pages);
@@ -2553,7 +2572,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 	unsigned long nr_soft_reclaimed;
 	unsigned long nr_soft_scanned;
 	gfp_t orig_mask;
-	enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
+	enum zone_type classzone_idx;
 
 	/*
 	 * If the number of buffer_heads in the machine exceeds the maximum
@@ -2561,17 +2580,23 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 	 * highmem pages could be pinning lowmem pages storing buffer_heads
 	 */
 	orig_mask = sc->gfp_mask;
-	if (buffer_heads_over_limit)
+	if (buffer_heads_over_limit) {
 		sc->gfp_mask |= __GFP_HIGHMEM;
+		sc->reclaim_idx = classzone_idx = gfp_zone(sc->gfp_mask);
+	}
 
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
-					gfp_zone(sc->gfp_mask), sc->nodemask) {
-		enum zone_type classzone_idx;
-
+					sc->reclaim_idx, sc->nodemask) {
 		if (!populated_zone(zone))
 			continue;
 
-		classzone_idx = requested_highidx;
+		/*
+		 * Note that reclaim_idx does not change as it is the highest
+		 * zone reclaimed from which for empty zones is a no-op but
+		 * classzone_idx is used by shrink_node to test if the slabs
+		 * should be shrunk on a given node.
+		 */
+		classzone_idx = sc->reclaim_idx;
 		while (!populated_zone(zone->zone_pgdat->node_zones +
 							classzone_idx))
 			classzone_idx--;
@@ -2600,8 +2625,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 			 */
 			if (IS_ENABLED(CONFIG_COMPACTION) &&
 			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
-			    zonelist_zone_idx(z) <= requested_highidx &&
-			    compaction_ready(zone, sc->order, requested_highidx)) {
+			    zonelist_zone_idx(z) <= classzone_idx &&
+			    compaction_ready(zone, sc->order, classzone_idx)) {
 				sc->compaction_ready = true;
 				continue;
 			}
@@ -2621,7 +2646,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 			/* need some check for avoid more shrink_zone() */
 		}
 
-		shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
+		shrink_node(zone->zone_pgdat, sc, classzone_idx);
 	}
 
 	/*
@@ -2847,6 +2872,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 	struct scan_control sc = {
 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
 		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
+		.reclaim_idx = gfp_zone(gfp_mask),
 		.order = order,
 		.nodemask = nodemask,
 		.priority = DEF_PRIORITY,
@@ -2886,6 +2912,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
 		.target_mem_cgroup = memcg,
 		.may_writepage = !laptop_mode,
 		.may_unmap = 1,
+		.reclaim_idx = MAX_NR_ZONES - 1,
 		.may_swap = !noswap,
 	};
 	unsigned long lru_pages;
@@ -2924,6 +2951,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
 		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
 				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
+		.reclaim_idx = MAX_NR_ZONES - 1,
 		.target_mem_cgroup = memcg,
 		.priority = DEF_PRIORITY,
 		.may_writepage = !laptop_mode,
@@ -3118,7 +3146,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
 						balance_gap, classzone_idx))
 		return true;
 
-	shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
+	shrink_node(zone->zone_pgdat, sc, classzone_idx);
 
 	/* TODO: ANOMALY */
 	clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
@@ -3167,6 +3195,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 	unsigned long nr_soft_scanned;
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
+		.reclaim_idx = MAX_NR_ZONES - 1,
 		.order = order,
 		.priority = DEF_PRIORITY,
 		.may_writepage = !laptop_mode,
@@ -3237,15 +3266,14 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 			sc.may_writepage = 1;
 
 		/*
-		 * Now scan the zone in the dma->highmem direction, stopping
-		 * at the last zone which needs scanning.
-		 *
-		 * We do this because the page allocator works in the opposite
-		 * direction.  This prevents the page allocator from allocating
-		 * pages behind kswapd's direction of progress, which would
-		 * cause too much scanning of the lower zones.
+		 * Continue scanning in the highmem->dma direction stopping at
+		 * the last zone which needs scanning. This may reclaim lowmem
+		 * pages that are not necessary for zone balancing but it
+		 * preserves LRU ordering. It is assumed that the bulk of
+		 * allocation requests can use arbitrary zones with the
+		 * possible exception of big highmem:lowmem configurations.
 		 */
-		for (i = 0; i <= end_zone; i++) {
+		for (i = end_zone; i >= 0; i--) {
 			struct zone *zone = pgdat->node_zones + i;
 
 			if (!populated_zone(zone))
@@ -3256,6 +3284,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 				continue;
 
 			sc.nr_scanned = 0;
+			sc.reclaim_idx = i;
 
 			nr_soft_scanned = 0;
 			/*
@@ -3513,6 +3542,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
 	struct scan_control sc = {
 		.nr_to_reclaim = nr_to_reclaim,
 		.gfp_mask = GFP_HIGHUSER_MOVABLE,
+		.reclaim_idx = MAX_NR_ZONES - 1,
 		.priority = DEF_PRIORITY,
 		.may_writepage = 1,
 		.may_unmap = 1,
@@ -3704,6 +3734,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
 		.may_unmap = !!(zone_reclaim_mode & RECLAIM_UNMAP),
 		.may_swap = 1,
+		.reclaim_idx = zone_idx(zone),
 	};
 
 	cond_resched();
@@ -3723,7 +3754,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 		 * priorities until we have enough memory freed.
 		 */
 		do {
-			shrink_zone(zone, &sc, true);
+			shrink_node(zone->zone_pgdat, &sc, zone_idx(zone));
 		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
 	}
 
-- 
2.6.4

[toc] | [next] | [standalone]

#1438045 — Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

On Fri, Jul 01, 2016 at 09:01:12PM +0100, Mel Gorman wrote:
> This patch makes reclaim decisions on a per-node basis.  A reclaimer knows
> what zone is required by the allocation request and skips pages from
> higher zones.  In many cases this will be ok because it's a GFP_HIGHMEM
> request of some description.  On 64-bit, ZONE_DMA32 requests will cause
> some problems but 32-bit devices on 64-bit platforms are increasingly
> rare.  Historically it would have been a major problem on 32-bit with big
> Highmem:Lowmem ratios but such configurations are also now rare and even
> where they exist, they are not encouraged.  If it really becomes a
> problem, it'll manifest as very low reclaim efficiencies.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
>  mm/vmscan.c | 79 ++++++++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 55 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 86a523a761c9..766b36bec829 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -84,6 +84,9 @@ struct scan_control {
>  	/* Scan (total_size >> priority) pages at once */
>  	int priority;
>  
> +	/* The highest zone to isolate pages for reclaim from */
> +	enum zone_type reclaim_idx;
> +
>  	unsigned int may_writepage:1;
>  
>  	/* Can mapped pages be reclaimed? */
> @@ -1392,6 +1395,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  	unsigned long nr_taken = 0;
>  	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
>  	unsigned long scan, nr_pages;
> +	LIST_HEAD(pages_skipped);
>  
>  	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
>  					!list_empty(src); scan++) {
> @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  
>  		VM_BUG_ON_PAGE(!PageLRU(page), page);
>  
> +		if (page_zonenum(page) > sc->reclaim_idx) {
> +			list_move(&page->lru, &pages_skipped);
> +			continue;
> +		}
> +

Hello, Mel.

I think that we don't need to skip LRU pages in active list. What we'd
like to do is just skipping actual reclaim since it doesn't make
freepage that we need. It's unrelated to skip the page in active list.

And, I have a concern that if inactive LRU is full with higher zone's
LRU pages, reclaim with low reclaim_idx could be stuck. This would be
easily possible if fair zone allocation policy is removed because we
will allocate the page on higher zone first.

Thanks.

>  		switch (__isolate_lru_page(page, mode)) {
>  		case 0:
>  			nr_pages = hpage_nr_pages(page);
> @@ -1420,6 +1429,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  		}
>  	}
>  
> +	/*
> +	 * Splice any skipped pages to the start of the LRU list. Note that
> +	 * this disrupts the LRU order when reclaiming for lower zones but
> +	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
> +	 * scanning would soon rescan the same pages to skip and put the
> +	 * system at risk of premature OOM.
> +	 */
> +	if (!list_empty(&pages_skipped))
> +		list_splice(&pages_skipped, src);
>  	*nr_scanned = scan;
>  	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
>  				    nr_taken, mode, is_file_lru(lru));
> @@ -1589,7 +1607,7 @@ static int current_may_throttle(void)
>  }
>  
>  /*
> - * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
> + * shrink_inactive_list() is a helper for shrink_node().  It returns the number
>   * of reclaimed pages
>   */
>  static noinline_for_stack unsigned long
> @@ -2401,12 +2419,13 @@ static inline bool should_continue_reclaim(struct zone *zone,
>  	}
>  }
>  
> -static bool shrink_zone(struct zone *zone, struct scan_control *sc,
> -			bool is_classzone)
> +static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc,
> +			enum zone_type classzone_idx)
>  {
>  	struct reclaim_state *reclaim_state = current->reclaim_state;
>  	unsigned long nr_reclaimed, nr_scanned;
>  	bool reclaimable = false;
> +	struct zone *zone = &pgdat->node_zones[classzone_idx];
>  
>  	do {
>  		struct mem_cgroup *root = sc->target_mem_cgroup;
> @@ -2438,7 +2457,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
>  			shrink_zone_memcg(zone, memcg, sc, &lru_pages);
>  			zone_lru_pages += lru_pages;
>  
> -			if (memcg && is_classzone)
> +			if (!global_reclaim(sc))
>  				shrink_slab(sc->gfp_mask, zone_to_nid(zone),
>  					    memcg, sc->nr_scanned - scanned,
>  					    lru_pages);
> @@ -2469,7 +2488,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
>  		 * Shrink the slab caches in the same proportion that
>  		 * the eligible LRU pages were scanned.
>  		 */
> -		if (global_reclaim(sc) && is_classzone)
> +		if (global_reclaim(sc))
>  			shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
>  				    sc->nr_scanned - nr_scanned,
>  				    zone_lru_pages);
> @@ -2553,7 +2572,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  	unsigned long nr_soft_reclaimed;
>  	unsigned long nr_soft_scanned;
>  	gfp_t orig_mask;
> -	enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
> +	enum zone_type classzone_idx;
>  
>  	/*
>  	 * If the number of buffer_heads in the machine exceeds the maximum
> @@ -2561,17 +2580,23 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  	 * highmem pages could be pinning lowmem pages storing buffer_heads
>  	 */
>  	orig_mask = sc->gfp_mask;
> -	if (buffer_heads_over_limit)
> +	if (buffer_heads_over_limit) {
>  		sc->gfp_mask |= __GFP_HIGHMEM;
> +		sc->reclaim_idx = classzone_idx = gfp_zone(sc->gfp_mask);
> +	}
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> -					gfp_zone(sc->gfp_mask), sc->nodemask) {
> -		enum zone_type classzone_idx;
> -
> +					sc->reclaim_idx, sc->nodemask) {
>  		if (!populated_zone(zone))
>  			continue;
>  
> -		classzone_idx = requested_highidx;
> +		/*
> +		 * Note that reclaim_idx does not change as it is the highest
> +		 * zone reclaimed from which for empty zones is a no-op but
> +		 * classzone_idx is used by shrink_node to test if the slabs
> +		 * should be shrunk on a given node.
> +		 */
> +		classzone_idx = sc->reclaim_idx;
>  		while (!populated_zone(zone->zone_pgdat->node_zones +
>  							classzone_idx))
>  			classzone_idx--;
> @@ -2600,8 +2625,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  			 */
>  			if (IS_ENABLED(CONFIG_COMPACTION) &&
>  			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
> -			    zonelist_zone_idx(z) <= requested_highidx &&
> -			    compaction_ready(zone, sc->order, requested_highidx)) {
> +			    zonelist_zone_idx(z) <= classzone_idx &&
> +			    compaction_ready(zone, sc->order, classzone_idx)) {
>  				sc->compaction_ready = true;
>  				continue;
>  			}
> @@ -2621,7 +2646,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  			/* need some check for avoid more shrink_zone() */
>  		}
>  
> -		shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
> +		shrink_node(zone->zone_pgdat, sc, classzone_idx);
>  	}
>  
>  	/*
> @@ -2847,6 +2872,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>  	struct scan_control sc = {
>  		.nr_to_reclaim = SWAP_CLUSTER_MAX,
>  		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
> +		.reclaim_idx = gfp_zone(gfp_mask),
>  		.order = order,
>  		.nodemask = nodemask,
>  		.priority = DEF_PRIORITY,
> @@ -2886,6 +2912,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
>  		.target_mem_cgroup = memcg,
>  		.may_writepage = !laptop_mode,
>  		.may_unmap = 1,
> +		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.may_swap = !noswap,
>  	};
>  	unsigned long lru_pages;
> @@ -2924,6 +2951,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
>  		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
>  				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
> +		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.target_mem_cgroup = memcg,
>  		.priority = DEF_PRIORITY,
>  		.may_writepage = !laptop_mode,
> @@ -3118,7 +3146,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
>  						balance_gap, classzone_idx))
>  		return true;
>  
> -	shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
> +	shrink_node(zone->zone_pgdat, sc, classzone_idx);
>  
>  	/* TODO: ANOMALY */
>  	clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
> @@ -3167,6 +3195,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>  	unsigned long nr_soft_scanned;
>  	struct scan_control sc = {
>  		.gfp_mask = GFP_KERNEL,
> +		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.order = order,
>  		.priority = DEF_PRIORITY,
>  		.may_writepage = !laptop_mode,
> @@ -3237,15 +3266,14 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>  			sc.may_writepage = 1;
>  
>  		/*
> -		 * Now scan the zone in the dma->highmem direction, stopping
> -		 * at the last zone which needs scanning.
> -		 *
> -		 * We do this because the page allocator works in the opposite
> -		 * direction.  This prevents the page allocator from allocating
> -		 * pages behind kswapd's direction of progress, which would
> -		 * cause too much scanning of the lower zones.
> +		 * Continue scanning in the highmem->dma direction stopping at
> +		 * the last zone which needs scanning. This may reclaim lowmem
> +		 * pages that are not necessary for zone balancing but it
> +		 * preserves LRU ordering. It is assumed that the bulk of
> +		 * allocation requests can use arbitrary zones with the
> +		 * possible exception of big highmem:lowmem configurations.
>  		 */
> -		for (i = 0; i <= end_zone; i++) {
> +		for (i = end_zone; i >= 0; i--) {
>  			struct zone *zone = pgdat->node_zones + i;
>  
>  			if (!populated_zone(zone))
> @@ -3256,6 +3284,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>  				continue;
>  
>  			sc.nr_scanned = 0;
> +			sc.reclaim_idx = i;
>  
>  			nr_soft_scanned = 0;
>  			/*
> @@ -3513,6 +3542,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
>  	struct scan_control sc = {
>  		.nr_to_reclaim = nr_to_reclaim,
>  		.gfp_mask = GFP_HIGHUSER_MOVABLE,
> +		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.priority = DEF_PRIORITY,
>  		.may_writepage = 1,
>  		.may_unmap = 1,
> @@ -3704,6 +3734,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
>  		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
>  		.may_unmap = !!(zone_reclaim_mode & RECLAIM_UNMAP),
>  		.may_swap = 1,
> +		.reclaim_idx = zone_idx(zone),
>  	};
>  
>  	cond_resched();
> @@ -3723,7 +3754,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
>  		 * priorities until we have enough memory freed.
>  		 */
>  		do {
> -			shrink_zone(zone, &sc, true);
> +			shrink_node(zone->zone_pgdat, &sc, zone_idx(zone));
>  		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
>  	}
>  
> -- 
> 2.6.4
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[toc] | [prev] | [next] | [standalone]

#1438473 — Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
> > @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >  
> >  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> >  
> > +		if (page_zonenum(page) > sc->reclaim_idx) {
> > +			list_move(&page->lru, &pages_skipped);
> > +			continue;
> > +		}
> > +
> 
> I think that we don't need to skip LRU pages in active list. What we'd
> like to do is just skipping actual reclaim since it doesn't make
> freepage that we need. It's unrelated to skip the page in active list.
> 

Why?

The active aging is sometimes about simply aging the LRU list. Aging the
active list based on the timing of when a zone-constrained allocation arrives
potentially introduces the same zone-balancing problems we currently have
and applying them to node-lru.

> And, I have a concern that if inactive LRU is full with higher zone's
> LRU pages, reclaim with low reclaim_idx could be stuck.

That is an outside possibility but unlikely given that it would require
that all outstanding allocation requests are zone-contrained. If it happens
that a premature OOM is encountered while the active list is large then
inactive_list_is_low could take scan_control as a parameter and use a
different ratio for zone-contrained allocations if scan priority is elevated.

It would be preferred to have an actual test case for this so the
altered ratio can be tested instead of introducing code that may be
useless or dead.

-- 
Mel Gorman
SUSE Labs

[toc] | [prev] | [next] | [standalone]

#1439071 — Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

On Thu, Jul 07, 2016 at 10:48:08AM +0100, Mel Gorman wrote:
> On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
> > > @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> > >  
> > >  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> > >  
> > > +		if (page_zonenum(page) > sc->reclaim_idx) {
> > > +			list_move(&page->lru, &pages_skipped);
> > > +			continue;
> > > +		}
> > > +
> > 
> > I think that we don't need to skip LRU pages in active list. What we'd
> > like to do is just skipping actual reclaim since it doesn't make
> > freepage that we need. It's unrelated to skip the page in active list.
> > 
> 
> Why?
> 
> The active aging is sometimes about simply aging the LRU list. Aging the
> active list based on the timing of when a zone-constrained allocation arrives
> potentially introduces the same zone-balancing problems we currently have
> and applying them to node-lru.

Could you explain more? I don't understand why aging the active list
based on the timing of when a zone-constrained allocation arrives
introduces the zone-balancing problem again.

I think that if above logic is applied to both the active/inactive
list, it could cause zone-balancing problem. LRU pages on lower zone
can be resident on memory with more chance. What we want to do with
node-lru is aging all the lru pages equally as much as possible. So,
basically, we need to age active/inactive list regardless allocation
type. But, there is a possibility that zone-constrained allocation
would reclaim too many LRU pages unnecessarily to satisfy zone-constrained
allocation, so we need to implement skipping such a page. It can be
done by just skipping the page in inactive list.

> 
> > And, I have a concern that if inactive LRU is full with higher zone's
> > LRU pages, reclaim with low reclaim_idx could be stuck.
> 
> That is an outside possibility but unlikely given that it would require
> that all outstanding allocation requests are zone-contrained. If it happens

I'm not sure that it is outside possibility. It can also happens if there
is zone-contrained allocation requestor and parallel memory hogger. In
this case, memory would be reclaimed by memory hogger but memory hogger would
consume them again so inactive LRU is continually full with higher
zone's LRU pages and zone-contrained allocation requestor cannot
progress.

> that a premature OOM is encountered while the active list is large then
> inactive_list_is_low could take scan_control as a parameter and use a
> different ratio for zone-contrained allocations if scan priority is elevated.

It would work.

> It would be preferred to have an actual test case for this so the
> altered ratio can be tested instead of introducing code that may be
> useless or dead.

Yes, actual test case would be preferred. I will try to implement
an artificial test case by myself but I'm not sure when I can do it.

Thanks.

[toc] | [prev] | [next] | [standalone]

#1439266 — Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

On Fri, Jul 08, 2016 at 11:28:52AM +0900, Joonsoo Kim wrote:
> On Thu, Jul 07, 2016 at 10:48:08AM +0100, Mel Gorman wrote:
> > On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
> > > > @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> > > >  
> > > >  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> > > >  
> > > > +		if (page_zonenum(page) > sc->reclaim_idx) {
> > > > +			list_move(&page->lru, &pages_skipped);
> > > > +			continue;
> > > > +		}
> > > > +
> > > 
> > > I think that we don't need to skip LRU pages in active list. What we'd
> > > like to do is just skipping actual reclaim since it doesn't make
> > > freepage that we need. It's unrelated to skip the page in active list.
> > > 
> > 
> > Why?
> > 
> > The active aging is sometimes about simply aging the LRU list. Aging the
> > active list based on the timing of when a zone-constrained allocation arrives
> > potentially introduces the same zone-balancing problems we currently have
> > and applying them to node-lru.
> 
> Could you explain more? I don't understand why aging the active list
> based on the timing of when a zone-constrained allocation arrives
> introduces the zone-balancing problem again.
> 

I mispoke. Avoid rotation of the active list based on the timing of a
zone-constrained allocation is what I think potentially introduces problems.
If there are zone-constrained allocations aging the active list then I worry
that pages would be artificially preserved on the active list.  No matter
what we do, there is distortion of the aging for zone-constrained allocation
because right now, it may deactivate high zone pages sooner than expected.

> I think that if above logic is applied to both the active/inactive
> list, it could cause zone-balancing problem. LRU pages on lower zone
> can be resident on memory with more chance.

If anything, with node-based LRU, it's high zone pages that can be resident
on memory for longer but only if there are zone-constrained allocations.
If we always reclaim based on age regardless of allocation requirements
then there is a risk that high zones are reclaimed far earlier than expected.

Basically, whether we skip pages in the active list or not there are
distortions with page aging and the impact is workload dependent. Right now,
I see no clear advantage to special casing active aging.

If we suspect this is a problem in the future, it would be a simple matter
of adding an additional bool parameter to isolate_lru_pages.

> > > And, I have a concern that if inactive LRU is full with higher zone's
> > > LRU pages, reclaim with low reclaim_idx could be stuck.
> > 
> > That is an outside possibility but unlikely given that it would require
> > that all outstanding allocation requests are zone-contrained. If it happens
> 
> I'm not sure that it is outside possibility. It can also happens if there
> is zone-contrained allocation requestor and parallel memory hogger. In
> this case, memory would be reclaimed by memory hogger but memory hogger would
> consume them again so inactive LRU is continually full with higher
> zone's LRU pages and zone-contrained allocation requestor cannot
> progress.
> 

The same memory hogger will also be reclaiming the highmem pages and
reallocating highmem pages.

> > It would be preferred to have an actual test case for this so the
> > altered ratio can be tested instead of introducing code that may be
> > useless or dead.
> 
> Yes, actual test case would be preferred. I will try to implement
> an artificial test case by myself but I'm not sure when I can do it.
> 

That would be appreciated.

-- 
Mel Gorman
SUSE Labs

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web