[PATCH v2] mm: vmscan: scan until it founds eligible pages

From: Minchan Kim
Date: Wed May 10 2017 - 19:00:41 EST

Although there are a ton of free swap and anonymous LRU page
in elgible zones, OOM happened.

balloon invoked oom-killer: gfp_mask=0x17080c0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOTRACK), nodemask=(null), order=0, oom_score_adj=0
CPU: 7 PID: 1138 Comm: balloon Not tainted 4.11.0-rc6-mm1-zram-00289-ge228d67e9677-dirty #17
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
Call Trace:
dump_stack+0x65/0x87
dump_header.isra.19+0x8f/0x20f
? preempt_count_add+0x9e/0xb0
? _raw_spin_unlock_irqrestore+0x24/0x40
oom_kill_process+0x21d/0x3f0
? has_capability_noaudit+0x17/0x20
out_of_memory+0xd8/0x390
__alloc_pages_slowpath+0xbc1/0xc50
? anon_vma_interval_tree_insert+0x84/0x90
__alloc_pages_nodemask+0x1a5/0x1c0
pte_alloc_one+0x20/0x50
__pte_alloc+0x1e/0x110
__handle_mm_fault+0x919/0x960
handle_mm_fault+0x77/0x120
__do_page_fault+0x27a/0x550
trace_do_page_fault+0x43/0x150
do_async_page_fault+0x2c/0x90
async_page_fault+0x28/0x30
RIP: 0033:0x7fc4636bacb8
RSP: 002b:00007fff97c9c4c0 EFLAGS: 00010202
RAX: 00007fc3e818d000 RBX: 00007fc4639f8760 RCX: 00007fc46372e9ca
RDX: 0000000000101002 RSI: 0000000000101000 RDI: 0000000000000000
RBP: 0000000000100010 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000022 R11: 00000000000a3901 R12: 00007fc3e818d010
R13: 0000000000101000 R14: 00007fc4639f87b8 R15: 00007fc4639f87b8
Mem-Info:
active_anon:424716 inactive_anon:65314 isolated_anon:0
active_file:52 inactive_file:46 isolated_file:0
unevictable:0 dirty:27 writeback:0 unstable:0
slab_reclaimable:3967 slab_unreclaimable:4125
mapped:133 shmem:43 pagetables:1674 bounce:0
free:4637 free_pcp:225 free_cma:0
Node 0 active_anon:1698864kB inactive_anon:261256kB active_file:208kB inactive_file:184kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:532kB dirty:108kB writeback:0kB shmem:172kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
DMA free:7316kB min:32kB low:44kB high:56kB active_anon:8064kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:464kB slab_unreclaimable:40kB kernel_stack:0kB pagetables:24kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 992 992 1952
DMA32 free:9088kB min:2048kB low:3064kB high:4080kB active_anon:952176kB inactive_anon:0kB active_file:36kB inactive_file:0kB unevictable:0kB writepending:88kB present:1032192kB managed:1019388kB mlocked:0kB slab_reclaimable:13532kB slab_unreclaimable:16460kB kernel_stack:3552kB pagetables:6672kB bounce:0kB free_pcp:56kB local_pcp:24kB free_cma:0kB
lowmem_reserve[]: 0 0 0 959
Movable free:3644kB min:1980kB low:2960kB high:3940kB active_anon:738560kB inactive_anon:261340kB active_file:188kB inactive_file:640kB unevictable:0kB writepending:20kB present:1048444kB managed:1010816kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:832kB local_pcp:60kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0
DMA: 1*4kB (E) 0*8kB 18*16kB (E) 10*32kB (E) 10*64kB (E) 9*128kB (ME) 8*256kB (E) 2*512kB (E) 2*1024kB (E) 0*2048kB 0*4096kB = 7524kB
DMA32: 417*4kB (UMEH) 181*8kB (UMEH) 68*16kB (UMEH) 48*32kB (UMEH) 14*64kB (MH) 3*128kB (M) 1*256kB (H) 1*512kB (M) 2*1024kB (M) 0*2048kB 0*4096kB = 9836kB
Movable: 1*4kB (M) 1*8kB (M) 1*16kB (M) 1*32kB (M) 0*64kB 1*128kB (M) 2*256kB (M) 4*512kB (M) 1*1024kB (M) 0*2048kB 0*4096kB = 3772kB
378 total pagecache pages
17 pages in swap cache
Swap cache stats: add 17325, delete 17302, find 0/27
Free swap = 978940kB
Total swap = 1048572kB
524157 pages RAM
0 pages HighMem/MovableOnly
12629 pages reserved
0 pages cma reserved
0 pages hwpoisoned
[ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
[ 433] 0 433 4904 5 14 3 82 0 upstart-udev-br
[ 438] 0 438 12371 5 27 3 191 -1000 systemd-udevd

With investigation, skipping page of isolate_lru_pages makes reclaim
void because it returns zero nr_taken easily so LRU shrinking is
effectively nothing and just increases priority aggressively.
Finally, OOM happens.

The problem is that get_scan_count determines nr_to_scan with
eligible zones so although priority drops to zero, it couldn't
reclaim any pages if the LRU contains mostly ineligible pages.

get_scan_count:

size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
size = size >> sc->priority;

Assumes sc->priority is 0 and LRU list is as follows.

N-N-N-N-H-H-H-H-H-H-H-H-H-H-H-H-H-H-H-H

(Ie, small eligible pages are in the head of LRU but others are
almost ineligible pages)

In that case, size becomes 4 so VM want to scan 4 pages but 4 pages
from tail of the LRU are not eligible pages.
If get_scan_count counts skipped pages, it doesn't reclaim any pages
remained after scanning 4 pages so it ends up OOM happening.

This patch makes isolate_lru_pages try to scan pages until it
encounters eligible zones's pages.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
* from v1
* put more words in description and code
* drop unncessary pages_skipped list flushing

mm/vmscan.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5ebf468c5429..e051bf4a1144 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1449,7 +1449,7 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec,
*
* Appropriate locks must be held before calling this function.
*
- * @nr_to_scan: The number of pages to look through on the list.
+ * @nr_to_scan: The number of eligible pages to look through on the list.
* @lruvec: The LRU vector to pull pages from.
* @dst: The temp list to put pages on to.
* @nr_scanned: The number of pages that were scanned.
@@ -1469,11 +1469,13 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
unsigned long skipped = 0;
- unsigned long scan, nr_pages;
+ unsigned long scan, total_scan, nr_pages;
LIST_HEAD(pages_skipped);

- for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
- !list_empty(src); scan++) {
+ for (total_scan = scan = 0; scan < nr_to_scan &&
+ nr_taken < nr_to_scan &&
+ !list_empty(src);
+ total_scan++) {
struct page *page;

page = lru_to_page(src);
@@ -1487,6 +1489,13 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
continue;
}

+ /*
+ * Do not count skipped pages because it makes the function to
+ * return with none isolated pages if the LRU mostly contains
+ * ineligible pages so that VM cannot reclaim any pages and
+ * trigger premature OOM.
+ */
+ scan++;
switch (__isolate_lru_page(page, mode)) {
case 0:
nr_pages = hpage_nr_pages(page);
@@ -1524,9 +1533,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
skipped += nr_skipped[zid];
}
}
- *nr_scanned = scan;
+ *nr_scanned = total_scan;
trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
- scan, skipped, nr_taken, mode, lru);
+ total_scan, skipped, nr_taken, mode, lru);
update_lru_sizes(lruvec, lru, nr_zone_taken);
return nr_taken;
}
--
2.7.4