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

[Michal Hocko]

On Thu 11-05-17 08:00:32, Minchan Kim wrote:
> 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.
> 

Fixes: 3db65812d688 ("Revert "mm, vmscan: account for skipped pages as a partial scan"")
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> * 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
> 

-- 
Michal Hocko
SUSE Labs