On Mon, 6 Dec 2010 11:32:09 +0000
Mel Gorman <mel@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx>
> >
> > 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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