Re: [resend][PATCH] mm, vmscan: fix do_try_to_free_pages() livelock

[Minchan Kim <minchan@kernel.org>]

Hi KOSAKI,

Sorry for late response.
Let me ask a question about description.

On Thu, Jun 14, 2012 at 04:13:12AM -0400, kosaki.motohiro@gmail.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> Currently, do_try_to_free_pages() can enter livelock. Because of,
> now vmscan has two conflicted policies.
> 
> 1) kswapd sleep when it couldn't reclaim any page when reaching
>    priority 0. This is because to avoid kswapd() infinite
>    loop. That said, kswapd assume direct reclaim makes enough
>    free pages to use either regular page reclaim or oom-killer.
>    This logic makes kswapd -> direct-reclaim dependency.
> 2) direct reclaim continue to reclaim without oom-killer until
>    kswapd turn on zone->all_unreclaimble. This is because
>    to avoid too early oom-kill.
>    This logic makes direct-reclaim -> kswapd dependency.
> 
> In worst case, direct-reclaim may continue to page reclaim forever
> when kswapd sleeps forever.

I have tried imagined scenario you mentioned above with code level but
unfortunately I got failed.
If kswapd can't meet high watermark on order-0, it doesn't sleep if I don't miss something.
So if kswapd sleeps, it means we already have enough order-0 free pages.
Hmm, could you describe scenario you found in detail with code level?

Anyway, as I look at your patch, I can't find any problem.
I just want to understand scenario you mentioned completely in my head.
Maybe It can help making description clear.

Thanks.

> 
> We can't turn on zone->all_unreclaimable from direct reclaim path
> because direct reclaim path don't take any lock and this way is racy.
> 
> Thus this patch removes zone->all_unreclaimable field completely and
> recalculates zone reclaimable state every time.
> 
> Note: we can't take the idea that direct-reclaim see zone->pages_scanned
> directly and kswapd continue to use zone->all_unreclaimable. Because, it
> is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use
> zone->all_unreclaimable as a name) describes the detail.
> 
> Reported-by: Aaditya Kumar <aaditya.kumar.30@gmail.com>
> Reported-by: Ying Han <yinghan@google.com>
> Cc: Nick Piggin <npiggin@gmail.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Minchan Kim <minchan.kim@gmail.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> ---
>  include/linux/mm_inline.h |   19 +++++++++++++++++
>  include/linux/mmzone.h    |    2 +-
>  include/linux/vmstat.h    |    1 -
>  mm/page-writeback.c       |    2 +
>  mm/page_alloc.c           |    5 +--
>  mm/vmscan.c               |   48 ++++++++++++--------------------------------
>  mm/vmstat.c               |    3 +-
>  7 files changed, 39 insertions(+), 41 deletions(-)
> 
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 1397ccf..04f32e1 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -2,6 +2,7 @@
>  #define LINUX_MM_INLINE_H
>  
>  #include <linux/huge_mm.h>
> +#include <linux/swap.h>
>  
>  /**
>   * page_is_file_cache - should the page be on a file LRU or anon LRU?
> @@ -99,4 +100,22 @@ static __always_inline enum lru_list page_lru(struct page *page)
>  	return lru;
>  }
>  
> +static inline unsigned long zone_reclaimable_pages(struct zone *zone)
> +{
> +	int nr;
> +
> +	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
> +	     zone_page_state(zone, NR_INACTIVE_FILE);
> +
> +	if (nr_swap_pages > 0)
> +		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
> +		      zone_page_state(zone, NR_INACTIVE_ANON);
> +
> +	return nr;
> +}
> +
> +static inline bool zone_reclaimable(struct zone *zone)
> +{
> +	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
> +}
>  #endif
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2427706..9d2a720 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -368,7 +368,7 @@ struct zone {
>  	 * free areas of different sizes
>  	 */
>  	spinlock_t		lock;
> -	int                     all_unreclaimable; /* All pages pinned */
> +
>  #ifdef CONFIG_MEMORY_HOTPLUG
>  	/* see spanned/present_pages for more description */
>  	seqlock_t		span_seqlock;
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index 65efb92..9607256 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -140,7 +140,6 @@ static inline unsigned long zone_page_state_snapshot(struct zone *zone,
>  }
>  
>  extern unsigned long global_reclaimable_pages(void);
> -extern unsigned long zone_reclaimable_pages(struct zone *zone);
>  
>  #ifdef CONFIG_NUMA
>  /*
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 93d8d2f..d2d957f 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -34,6 +34,8 @@
>  #include <linux/syscalls.h>
>  #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
>  #include <linux/pagevec.h>
> +#include <linux/mm_inline.h>
> +
>  #include <trace/events/writeback.h>
>  
>  /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4403009..5716b00 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -59,6 +59,7 @@
>  #include <linux/prefetch.h>
>  #include <linux/migrate.h>
>  #include <linux/page-debug-flags.h>
> +#include <linux/mm_inline.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -638,7 +639,6 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  	int to_free = count;
>  
>  	spin_lock(&zone->lock);
> -	zone->all_unreclaimable = 0;
>  	zone->pages_scanned = 0;
>  
>  	while (to_free) {
> @@ -680,7 +680,6 @@ static void free_one_page(struct zone *zone, struct page *page, int order,
>  				int migratetype)
>  {
>  	spin_lock(&zone->lock);
> -	zone->all_unreclaimable = 0;
>  	zone->pages_scanned = 0;
>  
>  	__free_one_page(page, zone, order, migratetype);
> @@ -2870,7 +2869,7 @@ void show_free_areas(unsigned int filter)
>  			K(zone_page_state(zone, NR_BOUNCE)),
>  			K(zone_page_state(zone, NR_WRITEBACK_TEMP)),
>  			zone->pages_scanned,
> -			(zone->all_unreclaimable ? "yes" : "no")
> +		       (zone_reclaimable(zone) ? "yes" : "no")
>  			);
>  		printk("lowmem_reserve[]:");
>  		for (i = 0; i < MAX_NR_ZONES; i++)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eeb3bc9..033671c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1592,7 +1592,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	 * latencies, so it's better to scan a minimum amount there as
>  	 * well.
>  	 */
> -	if (current_is_kswapd() && zone->all_unreclaimable)
> +	if (current_is_kswapd() && !zone_reclaimable(zone))
>  		force_scan = true;
>  	if (!global_reclaim(sc))
>  		force_scan = true;
> @@ -1936,8 +1936,8 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  		if (global_reclaim(sc)) {
>  			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
>  				continue;
> -			if (zone->all_unreclaimable &&
> -					sc->priority != DEF_PRIORITY)
> +			if (!zone_reclaimable(zone) &&
> +			    sc->priority != DEF_PRIORITY)
>  				continue;	/* Let kswapd poll it */
>  			if (COMPACTION_BUILD) {
>  				/*
> @@ -1975,11 +1975,6 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  	return aborted_reclaim;
>  }
>  
> -static bool zone_reclaimable(struct zone *zone)
> -{
> -	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
> -}
> -
>  /* All zones in zonelist are unreclaimable? */
>  static bool all_unreclaimable(struct zonelist *zonelist,
>  		struct scan_control *sc)
> @@ -1993,7 +1988,7 @@ static bool all_unreclaimable(struct zonelist *zonelist,
>  			continue;
>  		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
>  			continue;
> -		if (!zone->all_unreclaimable)
> +		if (zone_reclaimable(zone))
>  			return false;
>  	}
>  
> @@ -2299,7 +2294,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>  		 * they must be considered balanced here as well if kswapd
>  		 * is to sleep
>  		 */
> -		if (zone->all_unreclaimable) {
> +		if (zone_reclaimable(zone)) {
>  			balanced += zone->present_pages;
>  			continue;
>  		}
> @@ -2393,8 +2388,7 @@ loop_again:
>  			if (!populated_zone(zone))
>  				continue;
>  
> -			if (zone->all_unreclaimable &&
> -			    sc.priority != DEF_PRIORITY)
> +			if (!zone_reclaimable(zone) && sc.priority != DEF_PRIORITY)
>  				continue;
>  
>  			/*
> @@ -2443,14 +2437,13 @@ loop_again:
>  		 */
>  		for (i = 0; i <= end_zone; i++) {
>  			struct zone *zone = pgdat->node_zones + i;
> -			int nr_slab, testorder;
> +			int testorder;
>  			unsigned long balance_gap;
>  
>  			if (!populated_zone(zone))
>  				continue;
>  
> -			if (zone->all_unreclaimable &&
> -			    sc.priority != DEF_PRIORITY)
> +			if (!zone_reclaimable(zone) && sc.priority != DEF_PRIORITY)
>  				continue;
>  
>  			sc.nr_scanned = 0;
> @@ -2497,12 +2490,11 @@ loop_again:
>  				shrink_zone(zone, &sc);
>  
>  				reclaim_state->reclaimed_slab = 0;
> -				nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
> +				shrink_slab(&shrink, sc.nr_scanned, lru_pages);
>  				sc.nr_reclaimed += reclaim_state->reclaimed_slab;
>  				total_scanned += sc.nr_scanned;
>  
> -				if (nr_slab == 0 && !zone_reclaimable(zone))
> -					zone->all_unreclaimable = 1;
> +
>  			}
>  
>  			/*
> @@ -2514,7 +2506,7 @@ loop_again:
>  			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
>  				sc.may_writepage = 1;
>  
> -			if (zone->all_unreclaimable) {
> +			if (!zone_reclaimable(zone)) {
>  				if (end_zone && end_zone == i)
>  					end_zone--;
>  				continue;
> @@ -2616,7 +2608,7 @@ out:
>  			if (!populated_zone(zone))
>  				continue;
>  
> -			if (zone->all_unreclaimable &&
> +			if (!zone_reclaimable(zone) &&
>  			    sc.priority != DEF_PRIORITY)
>  				continue;
>  
> @@ -2850,20 +2842,6 @@ unsigned long global_reclaimable_pages(void)
>  	return nr;
>  }
>  
> -unsigned long zone_reclaimable_pages(struct zone *zone)
> -{
> -	int nr;
> -
> -	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
> -	     zone_page_state(zone, NR_INACTIVE_FILE);
> -
> -	if (nr_swap_pages > 0)
> -		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
> -		      zone_page_state(zone, NR_INACTIVE_ANON);
> -
> -	return nr;
> -}
> -
>  #ifdef CONFIG_HIBERNATION
>  /*
>   * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
> @@ -3158,7 +3136,7 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
>  	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
>  		return ZONE_RECLAIM_FULL;
>  
> -	if (zone->all_unreclaimable)
> +	if (!zone_reclaimable(zone))
>  		return ZONE_RECLAIM_FULL;
>  
>  	/*
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 1bbbbd9..94b9d4c 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -19,6 +19,7 @@
>  #include <linux/math64.h>
>  #include <linux/writeback.h>
>  #include <linux/compaction.h>
> +#include <linux/mm_inline.h>
>  
>  #ifdef CONFIG_VM_EVENT_COUNTERS
>  DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
> @@ -1022,7 +1023,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>  		   "\n  all_unreclaimable: %u"
>  		   "\n  start_pfn:         %lu"
>  		   "\n  inactive_ratio:    %u",
> -		   zone->all_unreclaimable,
> +		   !zone_reclaimable(zone),
>  		   zone->zone_start_pfn,
>  		   zone->inactive_ratio);
>  	seq_putc(m, '\n');
> -- 
> 1.7.1
> 

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