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