Re: [PATCH 1/5] mm: kswapd: Stop high-order balancing when any suitable zone is balanced

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 6 Dec 2010 11:32:09 +0000
Mel Gorman <mel@csn.ul.ie> wrote:

> On Mon, Dec 06, 2010 at 11:35:41AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Fri,  3 Dec 2010 11:45:30 +0000
> > Mel Gorman <mel@csn.ul.ie> wrote:
> > 
> > > When the allocator enters its slow path, kswapd is woken up to balance the
> > > node. It continues working until all zones within the node are balanced. For
> > > order-0 allocations, this makes perfect sense but for higher orders it can
> > > have unintended side-effects. If the zone sizes are imbalanced, kswapd may
> > > reclaim heavily within a smaller zone discarding an excessive number of
> > > pages. The user-visible behaviour is that kswapd is awake and reclaiming
> > > even though plenty of pages are free from a suitable zone.
> > > 
> > > This patch alters the "balance" logic for high-order reclaim allowing kswapd
> > > to stop if any suitable zone becomes balanced to reduce the number of pages
> > > it reclaims from other zones. kswapd still tries to ensure that order-0
> > > watermarks for all zones are met before sleeping.
> > > 
> > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > 
> > a nitpick.
> > 
> > > ---
> > >  include/linux/mmzone.h |    3 +-
> > >  mm/page_alloc.c        |    8 ++++--
> > >  mm/vmscan.c            |   55 +++++++++++++++++++++++++++++++++++++++++-------
> > >  3 files changed, 54 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > > index 39c24eb..7177f51 100644
> > > --- a/include/linux/mmzone.h
> > > +++ b/include/linux/mmzone.h
> > > @@ -645,6 +645,7 @@ typedef struct pglist_data {
> > >  	wait_queue_head_t kswapd_wait;
> > >  	struct task_struct *kswapd;
> > >  	int kswapd_max_order;
> > > +	enum zone_type classzone_idx;
> > >  } pg_data_t;
> > >  
> > >  #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
> > > @@ -660,7 +661,7 @@ typedef struct pglist_data {
> > >  
> > >  extern struct mutex zonelists_mutex;
> > >  void build_all_zonelists(void *data);
> > > -void wakeup_kswapd(struct zone *zone, int order);
> > > +void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx);
> > >  int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> > >  		int classzone_idx, int alloc_flags);
> > >  enum memmap_context {
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index e409270..82e3499 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1915,13 +1915,14 @@ __alloc_pages_high_priority(gfp_t gfp_mask, unsigned int order,
> > >  
> > >  static inline
> > >  void wake_all_kswapd(unsigned int order, struct zonelist *zonelist,
> > > -						enum zone_type high_zoneidx)
> > > +						enum zone_type high_zoneidx,
> > > +						enum zone_type classzone_idx)
> > >  {
> > >  	struct zoneref *z;
> > >  	struct zone *zone;
> > >  
> > >  	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx)
> > > -		wakeup_kswapd(zone, order);
> > > +		wakeup_kswapd(zone, order, classzone_idx);
> > >  }
> > >  
> > >  static inline int
> > > @@ -1998,7 +1999,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > >  		goto nopage;
> > >  
> > >  restart:
> > > -	wake_all_kswapd(order, zonelist, high_zoneidx);
> > > +	wake_all_kswapd(order, zonelist, high_zoneidx,
> > > +						zone_idx(preferred_zone));
> > >  
> > >  	/*
> > >  	 * OK, we're below the kswapd watermark and have kicked background
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index d31d7ce..d070d19 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -2165,11 +2165,14 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
> > >   * interoperates with the page allocator fallback scheme to ensure that aging
> > >   * of pages is balanced across the zones.
> > >   */
> > > -static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
> > > +static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> > > +							int classzone_idx)
> > >  {
> > >  	int all_zones_ok;
> > > +	int any_zone_ok;
> > >  	int priority;
> > >  	int i;
> > > +	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
> > >  	unsigned long total_scanned;
> > >  	struct reclaim_state *reclaim_state = current->reclaim_state;
> > >  	struct scan_control sc = {
> > > @@ -2192,7 +2195,6 @@ loop_again:
> > >  	count_vm_event(PAGEOUTRUN);
> > >  
> > >  	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
> > > -		int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
> > >  		unsigned long lru_pages = 0;
> > >  		int has_under_min_watermark_zone = 0;
> > >  
> > > @@ -2201,6 +2203,7 @@ loop_again:
> > >  			disable_swap_token();
> > >  
> > >  		all_zones_ok = 1;
> > > +		any_zone_ok = 0;
> > >  
> > >  		/*
> > >  		 * Scan in the highmem->dma direction for the highest
> > > @@ -2310,10 +2313,12 @@ loop_again:
> > >  				 * spectulatively avoid congestion waits
> > >  				 */
> > >  				zone_clear_flag(zone, ZONE_CONGESTED);
> > > +				if (i <= classzone_idx)
> > > +					any_zone_ok = 1;
> > >  			}
> > >  
> > >  		}
> > > -		if (all_zones_ok)
> > > +		if (all_zones_ok || (order && any_zone_ok))
> > >  			break;		/* kswapd: all done */
> > >  		/*
> > >  		 * OK, kswapd is getting into trouble.  Take a nap, then take
> > > @@ -2336,7 +2341,7 @@ loop_again:
> > >  			break;
> > >  	}
> > >  out:
> > > -	if (!all_zones_ok) {
> > > +	if (!(all_zones_ok || (order && any_zone_ok))) {
> > 
> > Could you add a comment ?
> > 
> > And this means...
> > 
> > 	all_zones_ok .... all_zone_balanced
> > 	any_zones_ok .... fallback_allocation_ok
> > ?
> > 
> 
> +
> +       /*
> +        * order-0: All zones must meet high watermark for a balanced node
> +        * high-order: Any zone below pgdats classzone_idx must meet the high
> +        *      watermark for a balanced node
> +        */
> 
> ?
> 
!

seems good. thanks.
-kame

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