[PATCH 1/2] mm: add per-zone lru list stat

[PATCH 1/2] mm: add per-zone lru list stat

[Minchan Kim]

While I did stress test with hackbench, I got OOM message frequently
which didn't ever happen in zone-lru.

gfp_mask=0x26004c0(GFP_KERNEL|__GFP_REPEAT|__GFP_NOTRACK), order=0
..
..
 [<c71a76e2>] __alloc_pages_nodemask+0xe52/0xe60
 [<c71f31dc>] ? new_slab+0x39c/0x3b0
 [<c71f31dc>] new_slab+0x39c/0x3b0
 [<c71f4eca>] ___slab_alloc.constprop.87+0x6da/0x840
 [<c763e6fc>] ? __alloc_skb+0x3c/0x260
 [<c777e127>] ? _raw_spin_unlock_irq+0x27/0x60
 [<c70cebfc>] ? trace_hardirqs_on_caller+0xec/0x1b0
 [<c70a1506>] ? finish_task_switch+0xa6/0x220
 [<c7219ee0>] ? poll_select_copy_remaining+0x140/0x140
 [<c7201645>] __slab_alloc.isra.81.constprop.86+0x40/0x6d
 [<c763e6fc>] ? __alloc_skb+0x3c/0x260
 [<c71f525c>] kmem_cache_alloc+0x22c/0x260
 [<c763e6fc>] ? __alloc_skb+0x3c/0x260
 [<c763e6fc>] __alloc_skb+0x3c/0x260
 [<c763eece>] alloc_skb_with_frags+0x4e/0x1a0
 [<c7638d6a>] sock_alloc_send_pskb+0x16a/0x1b0
 [<c770b581>] ? wait_for_unix_gc+0x31/0x90
 [<c71cfb1d>] ? alloc_set_pte+0x2ad/0x310
 [<c77084dd>] unix_stream_sendmsg+0x28d/0x340
 [<c7634dad>] sock_sendmsg+0x2d/0x40
 [<c7634e2c>] sock_write_iter+0x6c/0xc0
 [<c7204a90>] __vfs_write+0xc0/0x120
 [<c72053ab>] vfs_write+0x9b/0x1a0
 [<c71cc4a9>] ? __might_fault+0x49/0xa0
 [<c72062c4>] SyS_write+0x44/0x90
 [<c70036c6>] do_fast_syscall_32+0xa6/0x1e0
 [<c777ea2c>] sysenter_past_esp+0x45/0x74

Mem-Info:
active_anon:104698 inactive_anon:105791 isolated_anon:192
 active_file:433 inactive_file:283 isolated_file:22
 unevictable:0 dirty:0 writeback:296 unstable:0
 slab_reclaimable:6389 slab_unreclaimable:78927
 mapped:474 shmem:0 pagetables:101426 bounce:0
 free:10518 free_pcp:334 free_cma:0
Node 0 active_anon:418792kB inactive_anon:423164kB active_file:1732kB inactive_file:1132kB unevictable:0kB isolated(anon):768kB isolated(file):88kB mapped:1896kB dirty:0kB writeback:1184kB shmem:0kB writeback_tmp:0kB unstable:0kB pages_scanned:1478632 all_unreclaimable? yes
DMA free:3304kB min:68kB low:84kB high:100kB present:15992kB managed:15916kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:4088kB kernel_stack:0kB pagetables:2480kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 809 1965 1965
Normal free:3436kB min:3604kB low:4504kB high:5404kB present:897016kB managed:858460kB mlocked:0kB slab_reclaimable:25556kB slab_unreclaimable:311712kB kernel_stack:164608kB pagetables:30844kB bounce:0kB free_pcp:620kB local_pcp:104kB free_cma:0kB
lowmem_reserve[]: 0 0 9247 9247
HighMem free:33808kB min:512kB low:1796kB high:3080kB present:1183736kB managed:1183736kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:372252kB bounce:0kB free_pcp:428kB local_pcp:72kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0
DMA: 2*4kB (UM) 2*8kB (UM) 0*16kB 1*32kB (U) 1*64kB (U) 2*128kB (UM) 1*256kB (U) 1*512kB (M) 0*1024kB 1*2048kB (U) 0*4096kB = 3192kB
Normal: 33*4kB (MH) 79*8kB (ME) 11*16kB (M) 4*32kB (M) 2*64kB (ME) 2*128kB (EH) 7*256kB (EH) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3244kB
HighMem: 2590*4kB (UM) 1568*8kB (UM) 491*16kB (UM) 60*32kB (UM) 6*64kB (M) 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 33064kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
25121 total pagecache pages
24160 pages in swap cache
Swap cache stats: add 86371, delete 62211, find 42865/60187
Free swap  = 4015560kB
Total swap = 4192252kB
524186 pages RAM
295934 pages HighMem/MovableOnly
9658 pages reserved
0 pages cma reserved

The order-0 allocation for normal zone failed while there are a lot of
reclaimable memory(i.e., anonymous memory with free swap). I wanted to
analyze the problem but it was hard because we removed per-zone lru stat
so I couldn't know how many of anonymous memory there are in normal/dma
zone.

When we investigate OOM problem, reclaimable memory count is crucial stat
to find a problem. Without it, it's hard to parse the OOM message so I
believe we should keep it.

With per-zone lru stat,

gfp_mask=0x26004c0(GFP_KERNEL|__GFP_REPEAT|__GFP_NOTRACK), order=0
Mem-Info:
active_anon:101103 inactive_anon:102219 isolated_anon:0
 active_file:503 inactive_file:544 isolated_file:0
 unevictable:0 dirty:0 writeback:34 unstable:0
 slab_reclaimable:6298 slab_unreclaimable:74669
 mapped:863 shmem:0 pagetables:100998 bounce:0
 free:23573 free_pcp:1861 free_cma:0
Node 0 active_anon:404412kB inactive_anon:409040kB active_file:2012kB inactive_file:2176kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:3452kB dirty:0kB writeback:136kB shmem:0kB writeback_tmp:0kB unstable:0kB pages_scanned:1320845 all_unreclaimable? yes
DMA free:3296kB min:68kB low:84kB high:100kB active_anon:5540kB inactive_anon:0kB active_file:0kB inactive_file:0kB present:15992kB managed:15916kB mlocked:0kB slab_reclaimable:248kB slab_unreclaimable:2628kB kernel_stack:792kB pagetables:2316kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 809 1965 1965
Normal free:3600kB min:3604kB low:4504kB high:5404kB active_anon:86304kB inactive_anon:0kB active_file:160kB inactive_file:376kB present:897016kB managed:858524kB mlocked:0kB slab_reclaimable:24944kB slab_unreclaimable:296048kB kernel_stack:163832kB pagetables:35892kB bounce:0kB free_pcp:3076kB local_pcp:656kB free_cma:0kB
lowmem_reserve[]: 0 0 9247 9247
HighMem free:86156kB min:512kB low:1796kB high:3080kB active_anon:312852kB inactive_anon:410024kB active_file:1924kB inactive_file:2012kB present:1183736kB managed:1183736kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:365784kB bounce:0kB free_pcp:3868kB local_pcp:720kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0
DMA: 8*4kB (UM) 8*8kB (UM) 4*16kB (M) 2*32kB (UM) 2*64kB (UM) 1*128kB (M) 3*256kB (UME) 2*512kB (UE) 1*1024kB (E) 0*2048kB 0*4096kB = 3296kB
Normal: 240*4kB (UME) 160*8kB (UME) 23*16kB (ME) 3*32kB (UE) 3*64kB (UME) 2*128kB (ME) 1*256kB (U) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3408kB
HighMem: 10942*4kB (UM) 3102*8kB (UM) 866*16kB (UM) 76*32kB (UM) 11*64kB (UM) 4*128kB (UM) 1*256kB (M) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 86344kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
54409 total pagecache pages
53215 pages in swap cache
Swap cache stats: add 300982, delete 247765, find 157978/226539
Free swap  = 3803244kB
Total swap = 4192252kB
524186 pages RAM
295934 pages HighMem/MovableOnly
9642 pages reserved
0 pages cma reserved

With that, we can see normal zone has a 86M reclaimable memory so we can
know something goes wrong(I will fix the problem in next patch) in reclaim.

Of course, with restored per-zone lru stat, we can revert approximation
[1] did but intentionally, I don't touch it now and will do after getting
comment.

[1] mm, vmstat: remove zone and node double accounting by approximating retries

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/mm_inline.h | 2 ++
 include/linux/mmzone.h    | 5 +++++
 mm/page_alloc.c           | 8 ++++++++
 mm/vmstat.c               | 4 ++++
 4 files changed, 19 insertions(+)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index bcc4ed0..9cc130f 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -45,6 +45,8 @@ static __always_inline void __update_lru_size(struct lruvec *lruvec,
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 
 	__mod_node_page_state(pgdat, NR_LRU_BASE + lru, nr_pages);
+	__mod_zone_page_state(&pgdat->node_zones[zid],
+				NR_ZONE_LRU_BASE + lru, nr_pages);
 	acct_highmem_file_pages(zid, lru, nr_pages);
 }
 
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e6aca07..bbba91c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -110,6 +110,11 @@ struct zone_padding {
 enum zone_stat_item {
 	/* First 128 byte cacheline (assuming 64 bit words) */
 	NR_FREE_PAGES,
+	NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
+	NR_ZONE_INACTIVE_ANON = NR_ZONE_LRU_BASE,
+	NR_ZONE_ACTIVE_ANON,
+	NR_ZONE_INACTIVE_FILE,
+	NR_ZONE_ACTIVE_FILE,
 	NR_MLOCK,		/* mlock()ed pages found and moved off LRU */
 	NR_SLAB_RECLAIMABLE,
 	NR_SLAB_UNRECLAIMABLE,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 830ad49..1947dc5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4388,6 +4388,10 @@ void show_free_areas(unsigned int filter)
 			" min:%lukB"
 			" low:%lukB"
 			" high:%lukB"
+			" active_anon:%lukB"
+			" inactive_anon:%lukB"
+			" active_file:%lukB"
+			" inactive_file:%lukB"
 			" present:%lukB"
 			" managed:%lukB"
 			" mlocked:%lukB"
@@ -4405,6 +4409,10 @@ void show_free_areas(unsigned int filter)
 			K(min_wmark_pages(zone)),
 			K(low_wmark_pages(zone)),
 			K(high_wmark_pages(zone)),
+			K(zone_page_state(zone, NR_ZONE_ACTIVE_ANON)),
+			K(zone_page_state(zone, NR_ZONE_INACTIVE_ANON)),
+			K(zone_page_state(zone, NR_ZONE_ACTIVE_FILE)),
+			K(zone_page_state(zone, NR_ZONE_INACTIVE_FILE)),
 			K(zone->present_pages),
 			K(zone->managed_pages),
 			K(zone_page_state(zone, NR_MLOCK)),
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 91ecca9..b263484 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -921,6 +921,10 @@ int fragmentation_index(struct zone *zone, unsigned int order)
 const char * const vmstat_text[] = {
 	/* enum zone_stat_item countes */
 	"nr_free_pages",
+	"nr_inactive_anon",
+	"nr_active_anon",
+	"nr_inactive_file",
+	"nr_active_file",
 	"nr_mlock",
 	"nr_slab_reclaimable",
 	"nr_slab_unreclaimable",
-- 
1.9.1

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[PATCH 2/2] mm: consider per-zone inactive ratio to deactivate

[Minchan Kim]

With per-zone lru stat, we could know normal zone has 86M anonymous
memory but OOM happend with non-atomic order-0 allocation. And most of
anonymous pages in normal zone are on active list.

gfp_mask=0x26004c0(GFP_KERNEL|__GFP_REPEAT|__GFP_NOTRACK), order=0
Call Trace:
 [<c51a76e2>] __alloc_pages_nodemask+0xe52/0xe60
 [<c51f31dc>] ? new_slab+0x39c/0x3b0
 [<c51f31dc>] new_slab+0x39c/0x3b0
 [<c51f4eca>] ___slab_alloc.constprop.87+0x6da/0x840
 [<c563e6fc>] ? __alloc_skb+0x3c/0x260
 [<c50b8e93>] ? enqueue_task_fair+0x73/0xbf0
 [<c5219ee0>] ? poll_select_copy_remaining+0x140/0x140
 [<c5201645>] __slab_alloc.isra.81.constprop.86+0x40/0x6d
 [<c563e6fc>] ? __alloc_skb+0x3c/0x260
 [<c51f525c>] kmem_cache_alloc+0x22c/0x260
 [<c563e6fc>] ? __alloc_skb+0x3c/0x260
 [<c563e6fc>] __alloc_skb+0x3c/0x260
 [<c563eece>] alloc_skb_with_frags+0x4e/0x1a0
 [<c5638d6a>] sock_alloc_send_pskb+0x16a/0x1b0
 [<c570b581>] ? wait_for_unix_gc+0x31/0x90
 [<c57084dd>] unix_stream_sendmsg+0x28d/0x340
 [<c5634dad>] sock_sendmsg+0x2d/0x40
 [<c5634e2c>] sock_write_iter+0x6c/0xc0
 [<c5204a90>] __vfs_write+0xc0/0x120
 [<c52053ab>] vfs_write+0x9b/0x1a0
 [<c51cc4a9>] ? __might_fault+0x49/0xa0
 [<c52062c4>] SyS_write+0x44/0x90
 [<c50036c6>] do_fast_syscall_32+0xa6/0x1e0

Mem-Info:
active_anon:101103 inactive_anon:102219 isolated_anon:0
 active_file:503 inactive_file:544 isolated_file:0
 unevictable:0 dirty:0 writeback:34 unstable:0
 slab_reclaimable:6298 slab_unreclaimable:74669
 mapped:863 shmem:0 pagetables:100998 bounce:0
 free:23573 free_pcp:1861 free_cma:0
Node 0 active_anon:404412kB inactive_anon:409040kB active_file:2012kB inactive_file:2176kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:3452kB dirty:0kB writeback:136kB shmem:0kB writeback_tmp:0kB unstable:0kB pages_scanned:1320845 all_unreclaimable? yes
DMA free:3296kB min:68kB low:84kB high:100kB active_anon:5540kB inactive_anon:0kB active_file:0kB inactive_file:0kB present:15992kB managed:15916kB mlocked:0kB slab_reclaimable:248kB slab_unreclaimable:2628kB kernel_stack:792kB pagetables:2316kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 809 1965 1965
Normal free:3600kB min:3604kB low:4504kB high:5404kB active_anon:86304kB inactive_anon:0kB active_file:160kB inactive_file:376kB present:897016kB managed:858524kB mlocked:0kB slab_reclaimable:24944kB slab_unreclaimable:296048kB kernel_stack:163832kB pagetables:35892kB bounce:0kB free_pcp:3076kB local_pcp:656kB free_cma:0kB
lowmem_reserve[]: 0 0 9247 9247
HighMem free:86156kB min:512kB low:1796kB high:3080kB active_anon:312852kB inactive_anon:410024kB active_file:1924kB inactive_file:2012kB present:1183736kB managed:1183736kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:365784kB bounce:0kB free_pcp:3868kB local_pcp:720kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0
DMA: 8*4kB (UM) 8*8kB (UM) 4*16kB (M) 2*32kB (UM) 2*64kB (UM) 1*128kB (M) 3*256kB (UME) 2*512kB (UE) 1*1024kB (E) 0*2048kB 0*4096kB = 3296kB
Normal: 240*4kB (UME) 160*8kB (UME) 23*16kB (ME) 3*32kB (UE) 3*64kB (UME) 2*128kB (ME) 1*256kB (U) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 3408kB
HighMem: 10942*4kB (UM) 3102*8kB (UM) 866*16kB (UM) 76*32kB (UM) 11*64kB (UM) 4*128kB (UM) 1*256kB (M) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 86344kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
54409 total pagecache pages
53215 pages in swap cache
Swap cache stats: add 300982, delete 247765, find 157978/226539
Free swap  = 3803244kB
Total swap = 4192252kB
524186 pages RAM
295934 pages HighMem/MovableOnly
9642 pages reserved
0 pages cma reserved

The problem was current deactivation logic(i.e., inactive_list_is_low).

	Node 0 active_anon:404412kB inactive_anon:409040kB

IOW, (inactive_anon of node * inactive_ratio > active_anon of node) due
to highmem anonymous stat so VM never deactivates normal zone's
anonymous pages.

This patch makes inactive_list_is_low be aware of per-zone inactive raio
so if requested zone or lower zones's LRU list cannot meet the ratio, VM
start to deactivate pages.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/vmscan.c | 41 ++++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index dffa7e0..e60329b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1955,12 +1955,16 @@ static void shrink_active_list(unsigned long nr_to_scan,
  *    1TB     101        10GB
  *   10TB     320        32GB
  */
-static bool inactive_list_is_low(struct lruvec *lruvec, bool file)
+static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
+						int classzone_idx)
 {
 	unsigned long inactive_ratio;
 	unsigned long inactive;
 	unsigned long active;
 	unsigned long gb;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	struct zone *zone;
+	int zone_idx;
 
 	/*
 	 * If we don't have swap space, anonymous page deactivation
@@ -1969,23 +1973,34 @@ static bool inactive_list_is_low(struct lruvec *lruvec, bool file)
 	if (!file && !total_swap_pages)
 		return false;
 
-	inactive = lruvec_lru_size(lruvec, file * LRU_FILE);
-	active = lruvec_lru_size(lruvec, file * LRU_FILE + LRU_ACTIVE);
+	for (zone_idx = classzone_idx; zone_idx > 0; zone_idx--) {
+		zone = &pgdat->node_zones[zone_idx];
+		if (!populated_zone(zone))
+			continue;
 
-	gb = (inactive + active) >> (30 - PAGE_SHIFT);
-	if (gb)
-		inactive_ratio = int_sqrt(10 * gb);
-	else
-		inactive_ratio = 1;
+		inactive = zone_page_state(zone,
+				NR_ZONE_LRU_BASE + file * LRU_FILE);
+		active = zone_page_state(zone,
+				NR_ZONE_LRU_BASE + file * LRU_FILE + LRU_ACTIVE);
 
-	return inactive * inactive_ratio < active;
+		gb = (inactive + active) >> (30 - PAGE_SHIFT);
+		if (gb)
+			inactive_ratio = int_sqrt(10 * gb);
+		else
+			inactive_ratio = 1;
+
+		if ((inactive * inactive_ratio) < active)
+			return true;
+	}
+
+	return false;
 }
 
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 				 struct lruvec *lruvec, struct scan_control *sc)
 {
 	if (is_active_lru(lru)) {
-		if (inactive_list_is_low(lruvec, is_file_lru(lru)))
+		if (inactive_list_is_low(lruvec, is_file_lru(lru), sc->reclaim_idx))
 			shrink_active_list(nr_to_scan, lruvec, sc, lru);
 		return 0;
 	}
@@ -2116,7 +2131,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 	 * lruvec even if it has plenty of old anonymous pages unless the
 	 * system is under heavy pressure.
 	 */
-	if (!inactive_list_is_low(lruvec, true) &&
+	if (!inactive_list_is_low(lruvec, true, sc->reclaim_idx) &&
 	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
 		scan_balance = SCAN_FILE;
 		goto out;
@@ -2358,7 +2373,7 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
 	 * Even if we did not try to evict anon pages at all, we want to
 	 * rebalance the anon lru active/inactive ratio.
 	 */
-	if (inactive_list_is_low(lruvec, false))
+	if (inactive_list_is_low(lruvec, false, sc->reclaim_idx))
 		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
 				   sc, LRU_ACTIVE_ANON);
 
@@ -3011,7 +3026,7 @@ static void age_active_anon(struct pglist_data *pgdat,
 	do {
 		struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
 
-		if (inactive_list_is_low(lruvec, false))
+		if (inactive_list_is_low(lruvec, false, sc->reclaim_idx))
 			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
 					   sc, LRU_ACTIVE_ANON);
 
-- 
1.9.1

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Re: [PATCH 1/2] mm: add per-zone lru list stat

[Mel Gorman]

On Wed, Jul 20, 2016 at 12:50:32AM +0900, Minchan Kim wrote:
> While I did stress test with hackbench, I got OOM message frequently
> which didn't ever happen in zone-lru.
> 

This one also showed pgdat going unreclaimable early. Have you tried any
of the three oom-related patches I sent to Joonsoo to see what impact,
if any, it had?

-- 
Mel Gorman
SUSE Labs

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Re: [PATCH 1/2] mm: add per-zone lru list stat

[Minchan Kim]

On Tue, Jul 19, 2016 at 05:48:57PM +0100, Mel Gorman wrote:
> On Wed, Jul 20, 2016 at 12:50:32AM +0900, Minchan Kim wrote:
> > While I did stress test with hackbench, I got OOM message frequently
> > which didn't ever happen in zone-lru.
> > 
> 
> This one also showed pgdat going unreclaimable early. Have you tried any
> of the three oom-related patches I sent to Joonsoo to see what impact,
> if any, it had?

Before the result, I want to say goal of this patch, again.
Without per-zone lru stat, it's really hard to debug OOM problem in
multiple zones system so regardless of solving the problem, we should add
per-zone lru stat for debuggability of OOM which has been never perfect
solution, ever.

You sent 3 patches in that thread and first one was same I had applied
when I found this problem firstly. It didn't solve the problem.

So I tested last one

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a6f31617a08c..0dc443b52228 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1415,7 +1415,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	LIST_HEAD(pages_skipped);
 
 	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
-					!list_empty(src); scan++) {
+					!list_empty(src);) {
 		struct page *page;
 
 		page = lru_to_page(src);
@@ -1428,6 +1428,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			nr_skipped[page_zonenum(page)]++;
 			continue;
 		}
+`
+		/* Pages skipped do not contribute to scan */
+		scan++;
 
 		switch (__isolate_lru_page(page, mode)) {
 		case 0:

The result is not OOM but hackbench stalls forever.
When I parse vmstat for every 2sec, I found pgskip_high velocity is too
high(i.e., 100000000 pages per 2 sec) while pgscan_direct and pgdeactiation is
really low(i.e., 30 pages per 2 sec).
The reason why it doesn't trigger OOM is a small amout of pages(i.e. 20 pages
per sec) are freed so NR_PAGES_SCANNED is always reset to zero.

> 
> -- 
> Mel Gorman
> SUSE Labs

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Re: [PATCH 1/2] mm: add per-zone lru list stat

[Mel Gorman]

On Wed, Jul 20, 2016 at 09:16:24AM +0900, Minchan Kim wrote:
> On Tue, Jul 19, 2016 at 05:48:57PM +0100, Mel Gorman wrote:
> > On Wed, Jul 20, 2016 at 12:50:32AM +0900, Minchan Kim wrote:
> > > While I did stress test with hackbench, I got OOM message frequently
> > > which didn't ever happen in zone-lru.
> > > 
> > 
> > This one also showed pgdat going unreclaimable early. Have you tried any
> > of the three oom-related patches I sent to Joonsoo to see what impact,
> > if any, it had?
> 
> Before the result, I want to say goal of this patch, again.
> Without per-zone lru stat, it's really hard to debug OOM problem in
> multiple zones system so regardless of solving the problem, we should add
> per-zone lru stat for debuggability of OOM which has been never perfect
> solution, ever.
> 

That's not in dispute, I simply wanted to know the impact.

> The result is not OOM but hackbench stalls forever.

Ok, that points to both the premature marking pgdats as unreclaimable
and the inactive rotation are both problems.

I have a series prepared that may or may not address the problem. I'm
trying to reproduce the OOM killer on a 32-bit KVM but so far so luck.
If I fail to reproduce it then I cannot tell if the series has an impact
and may have to post it and hope you and Joonsoo can test it.

-- 
Mel Gorman
SUSE Labs

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