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Message-ID: <c1383114-494b-e8ff-6bfe-73baf2786a0f@linux.alibaba.com>
Date: Thu, 14 Apr 2022 16:55:27 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Jagdish Gediya <jvgediya@...ux.ibm.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
dave.hansen@...ux.intel.com, ying.huang@...el.com
Subject: Re: [PATCH v2 1/5] mm: demotion: Set demotion list differently
On 4/13/2022 5:22 PM, Jagdish Gediya wrote:
> Sharing used_targets between multiple nodes in a single
> pass limits some of the opportunities for demotion target
> sharing.
>
> Don't share the used targets between multiple nodes in a
> single pass, instead accumulate all the used targets in
> source nodes shared by all pass, and reset 'used_targets'
> to source nodes while finding demotion targets for any new
> node.
>
> This results into some more opportunities to share demotion
> targets between multiple source nodes, e.g. with below NUMA
> topology, where node 0 & 1 are cpu + dram nodes, node 2 & 3
> are equally slower memory only nodes, and node 4 is slowest
> memory only node,
>
> available: 5 nodes (0-4)
> node 0 cpus: 0 1
> node 0 size: n MB
> node 0 free: n MB
> node 1 cpus: 2 3
> node 1 size: n MB
> node 1 free: n MB
> node 2 cpus:
> node 2 size: n MB
> node 2 free: n MB
> node 3 cpus:
> node 3 size: n MB
> node 3 free: n MB
> node 4 cpus:
> node 4 size: n MB
> node 4 free: n MB
> node distances:
> node 0 1 2 3 4
> 0: 10 20 40 40 80
> 1: 20 10 40 40 80
> 2: 40 40 10 40 80
> 3: 40 40 40 10 80
> 4: 80 80 80 80 10
>
> The existing implementation gives below demotion targets,
>
> node demotion_target
> 0 3, 2
> 1 4
> 2 X
> 3 X
> 4 X
>
> With this patch applied, below are the demotion targets,
>
> node demotion_target
> 0 3, 2
> 1 3, 2
> 2 4
> 3 4
> 4 X
>
> e.g. with below NUMA topology, where node 0, 1 & 2 are
> cpu + dram nodes and node 3 is slow memory node,
>
> available: 4 nodes (0-3)
> node 0 cpus: 0 1
> node 0 size: n MB
> node 0 free: n MB
> node 1 cpus: 2 3
> node 1 size: n MB
> node 1 free: n MB
> node 2 cpus: 4 5
> node 2 size: n MB
> node 2 free: n MB
> node 3 cpus:
> node 3 size: n MB
> node 3 free: n MB
> node distances:
> node 0 1 2 3
> 0: 10 20 20 40
> 1: 20 10 20 40
> 2: 20 20 10 40
> 3: 40 40 40 10
>
> The existing implementation gives below demotion targets,
>
> node demotion_target
> 0 3
> 1 X
> 2 X
> 3 X
>
> With this patch applied, below are the demotion targets,
>
> node demotion_target
> 0 3
> 1 3
> 2 3
> 3 X
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Signed-off-by: Jagdish Gediya <jvgediya@...ux.ibm.com>
> ---
Looks reasonable to me. Please feel free to add:
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
Tested-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> mm/migrate.c | 25 ++++++++++++++-----------
> 1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index de175e2fdba5..516f4e1348c1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2383,7 +2383,7 @@ static void __set_migration_target_nodes(void)
> {
> nodemask_t next_pass = NODE_MASK_NONE;
> nodemask_t this_pass = NODE_MASK_NONE;
> - nodemask_t used_targets = NODE_MASK_NONE;
> + nodemask_t source_nodes = NODE_MASK_NONE;
> int node, best_distance;
>
> /*
> @@ -2401,20 +2401,23 @@ static void __set_migration_target_nodes(void)
> again:
> this_pass = next_pass;
> next_pass = NODE_MASK_NONE;
> +
> /*
> - * To avoid cycles in the migration "graph", ensure
> - * that migration sources are not future targets by
> - * setting them in 'used_targets'. Do this only
> - * once per pass so that multiple source nodes can
> - * share a target node.
> - *
> - * 'used_targets' will become unavailable in future
> - * passes. This limits some opportunities for
> - * multiple source nodes to share a destination.
> + * Accumulate source nodes to avoid the cycle in migration
> + * list.
> */
> - nodes_or(used_targets, used_targets, this_pass);
> + nodes_or(source_nodes, source_nodes, this_pass);
>
> for_each_node_mask(node, this_pass) {
> + /*
> + * To avoid cycles in the migration "graph", ensure
> + * that migration sources are not future targets by
> + * setting them in 'used_targets'. Reset used_targets
> + * to source nodes for each node in this pass so that
> + * multiple source nodes can share a target node.
> + */
> + nodemask_t used_targets = source_nodes;
> +
> best_distance = -1;
>
> /*
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