quoted text > 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
+ */
?
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
--
