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Re: [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit
Date 2016-06-22 16:50 +0200
Message-ID <rMRDA-4He-5@gated-at.bofh.it> (permalink)
References <rMuGZ-6Vn-3@gated-at.bofh.it> <rMv0l-71Y-17@gated-at.bofh.it>
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On Tue 21-06-16 15:15:59, Mel Gorman wrote:
> If buffer heads are over the limit then the direct reclaim gfp_mask
> is promoted to __GFP_HIGHMEM so that lowmem is indirectly freed. With
> node-based reclaim, it is also required that the classzone_idx be updated
> or the pages will be skipped.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/vmscan.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1f7c1262c0a3..f4c759b3581b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2571,8 +2571,10 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
>  	 * highmem pages could be pinning lowmem pages storing buffer_heads
>  	 */
>  	orig_mask = sc->gfp_mask;
> -	if (buffer_heads_over_limit)
> +	if (buffer_heads_over_limit) {
>  		sc->gfp_mask |= __GFP_HIGHMEM;
> +		classzone_idx = gfp_zone(sc->gfp_mask);
> +	}
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>  					gfp_zone(sc->gfp_mask), sc->nodemask) {

The code that follows that however does update classzone_idx
		/*
		 * Note that reclaim_idx does not change as it is the highest
		 * zone reclaimed from which for empty zones is a no-op but
		 * classzone_idx is used by shrink_node to test if the slabs
		 * should be shrunk on a given node.
		 */
		while (!populated_zone(zone->zone_pgdat->node_zones +
							classzone_idx)) {
			classzone_idx--;
		}

so if we start with a zone which doesn't have the highmem zone we will
not see highmems of other zone AFAIU. I guess this would be unlikely
because highmem systems will be UMA in most cases but the code looks a
bit confusing.

-- 
Michal Hocko
SUSE Labs

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[PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 07/27] mm, vmscan: Remove balance gap Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 09/27] mm, vmscan: By default have direct reclaim only shrink once per node Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 02/27] mm, vmscan: Move lru_lock to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 10/27] mm, vmscan: Remove duplicate logic clearing node congestion and dirty state Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is any eligible zone Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:20 +0200
  [PATCH 14/27] mm, workingset: Make working set detection node-aware Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
  [PATCH 17/27] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 17/27] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:30 +0200
  [PATCH 12/27] mm, vmscan: Make shrink_node decisions more node-centric Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 12/27] mm, vmscan: Make shrink_node decisions more  node-centric Michal Hocko <mhocko@kernel.org> - 2016-06-22 15:30 +0200
    Re: [PATCH 12/27] mm, vmscan: Make shrink_node decisions more  node-centric Vlastimil Babka <vbabka@suse.cz> - 2016-06-22 17:50 +0200
  [PATCH 16/27] mm: Move page mapped accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 16/27] mm: Move page mapped accounting to the node Andrew Morton <akpm@linux-foundation.org> - 2016-06-22 00:50 +0200
      Re: [PATCH 16/27] mm: Move page mapped accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 10:40 +0200
    Re: [PATCH 16/27] mm: Move page mapped accounting to the node Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:40 +0200
  [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones to nodes Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones  to nodes Michal Hocko <mhocko@kernel.org> - 2016-06-22 15:20 +0200
  [PATCH 22/27] mm: Convert zone_reclaim to node_reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
  [PATCH 19/27] mm: Move vmscan writes and file write accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 19/27] mm: Move vmscan writes and file write accounting  to the node Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:50 +0200
      Re: [PATCH 19/27] mm: Move vmscan writes and file write accounting  to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 16:00 +0200
        Re: [PATCH 19/27] mm: Move vmscan writes and file write accounting to  the node Vlastimil Babka <vbabka@suse.cz> - 2016-06-23 16:10 +0200
          Re: [PATCH 19/27] mm: Move vmscan writes and file write accounting  to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 18:10 +0200
  [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
  [PATCH 18/27] mm: Move most file-based accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:30 +0200
    Re: [PATCH 18/27] mm: Move most file-based accounting to the node Michal Hocko <mhocko@kernel.org> - 2016-06-22 17:30 +0200
  [PATCH 23/27] mm, vmscan: Add classzone information to tracepoints Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:40 +0200
  [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:40 +0200
    Re: [PATCH 20/27] mm, vmscan: Update classzone_idx if  buffer_heads_over_limit Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:50 +0200
  [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:40 +0200
  [PATCH 26/27] mm: vmstat: Replace __count_zone_vm_events with a zone id equivalent Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:40 +0200
  [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:40 +0200
    Re: [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms  of nodes Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:30 +0200
      Re: [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms  of nodes Michal Hocko <mhocko@kernel.org> - 2016-06-22 16:30 +0200
        Re: [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms  of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 15:00 +0200
          Re: [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms  of nodes Michal Hocko <mhocko@kernel.org> - 2016-06-23 15:20 +0200
  [PATCH 25/27] mm: page_alloc: Cache the last node whose dirty limit is reached Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:50 +0200
  [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone Mel Gorman <mgorman@techsingularity.net> - 2016-06-21 16:50 +0200
    Re: [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for  the requested classzone Vlastimil Babka <vbabka@suse.cz> - 2016-06-22 18:10 +0200
  Re: [PATCH 03/27] mm, vmscan: Move LRU lists to node Vlastimil Babka <vbabka@suse.cz> - 2016-06-22 15:00 +0200
  Re: [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 12:30 +0200
    Re: [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Michal Hocko <mhocko@kernel.org> - 2016-06-23 13:30 +0200
      Re: [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Mel Gorman <mgorman@techsingularity.net> - 2016-06-23 14:40 +0200
        Re: [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Michal Hocko <mhocko@kernel.org> - 2016-06-23 14:50 +0200

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