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Re: [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone

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  Re: [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-07-05 09:00 +0200
    Re: [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest  eligible zone Mel Gorman <mgorman@techsingularity.net> - 2016-07-05 12:50 +0200

#1436803 — Re: [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone

> 
> The ac_classzone_idx is used as the basis for waking kswapd and that is based
> on the preferred zoneref. If the preferred zoneref's highest zone is lower
> than what is available on other nodes, it's possible that kswapd is woken
> on a zone with only higher, but still eligible, zones. As classzone_idx
> is strictly adhered to now, it causes a problem because eligible pages
> are skipped.
> 
> For example, node 0 has only DMA32 and node 1 has only NORMAL. An allocating
> context running on node 0 may wake kswapd on node 1 telling it to skip
> all NORMAL pages.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>

>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2fe2fbb4f2ad..b10bee2e5968 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3415,7 +3415,7 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
>  	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
>  					ac->high_zoneidx, ac->nodemask) {
>  		if (last_pgdat != zone->zone_pgdat)
> -			wakeup_kswapd(zone, order, ac_classzone_idx(ac));
> +			wakeup_kswapd(zone, order, ac->high_zoneidx);
>  		last_pgdat = zone->zone_pgdat;
>  	}
>  }
> --
> 2.6.4

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#1436916 — Re: [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone

On Tue, Jul 05, 2016 at 02:57:38PM +0800, Hillf Danton wrote:
> > 
> > The ac_classzone_idx is used as the basis for waking kswapd and that is based
> > on the preferred zoneref. If the preferred zoneref's highest zone is lower
> > than what is available on other nodes, it's possible that kswapd is woken
> > on a zone with only higher, but still eligible, zones. As classzone_idx
> > is strictly adhered to now, it causes a problem because eligible pages
> > are skipped.
> > 
> > For example, node 0 has only DMA32 and node 1 has only NORMAL. An allocating
> > context running on node 0 may wake kswapd on node 1 telling it to skip
> > all NORMAL pages.
> > 
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > ---
> Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
> 

Thanks. I also noticed when applying the ack that "zoneref's highest
zone" should have been "zoneref's first zone" so fixed that too.

-- 
Mel Gorman
SUSE Labs

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