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From: "Huang\, Ying" <ying.huang@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <linux-kernel@vger.kernel.org>,  <linux-mm@kvack.org>,
	 <yang.shi@linux.alibaba.com>,  <rientjes@google.com>,
	 <dan.j.williams@intel.com>
Subject: Re: [RFC][PATCH 5/8] mm/numa: automatically generate node migration order
Date: Tue, 30 Jun 2020 16:22:46 +0800
Message-ID: <87ftadotd5.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20200629234512.F34EDC44@viggo.jf.intel.com> (Dave Hansen's message of "Mon, 29 Jun 2020 16:45:12 -0700")

Dave Hansen <dave.hansen@linux.intel.com> writes:

> +/*
> + * Find an automatic demotion target for 'node'.
> + * Failing here is OK.  It might just indicate
> + * being at the end of a chain.
> + */
> +static int establish_migrate_target(int node, nodemask_t *used)
> +{
> +	int migration_target;
> +
> +	/*
> +	 * Can not set a migration target on a
> +	 * node with it already set.
> +	 *
> +	 * No need for READ_ONCE() here since this
> +	 * in the write path for node_demotion[].
> +	 * This should be the only thread writing.
> +	 */
> +	if (node_demotion[node] != NUMA_NO_NODE)
> +		return NUMA_NO_NODE;
> +
> +	migration_target = find_next_best_node(node, used);
> +	if (migration_target == NUMA_NO_NODE)
> +		return NUMA_NO_NODE;
> +
> +	node_demotion[node] = migration_target;
> +
> +	return migration_target;
> +}
> +
> +/*
> + * When memory fills up on a node, memory contents can be
> + * automatically migrated to another node instead of
> + * discarded at reclaim.
> + *
> + * Establish a "migration path" which will start at nodes
> + * with CPUs and will follow the priorities used to build the
> + * page allocator zonelists.
> + *
> + * The difference here is that cycles must be avoided.  If
> + * node0 migrates to node1, then neither node1, nor anything
> + * node1 migrates to can migrate to node0.
> + *
> + * This function can run simultaneously with readers of
> + * node_demotion[].  However, it can not run simultaneously
> + * with itself.  Exclusion is provided by memory hotplug events
> + * being single-threaded.
> + */
> +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;
> +	int node;
> +
> +	get_online_mems();
> +	/*
> +	 * Avoid any oddities like cycles that could occur
> +	 * from changes in the topology.  This will leave
> +	 * a momentary gap when migration is disabled.
> +	 */
> +	disable_all_migrate_targets();
> +
> +	/*
> +	 * Ensure that the "disable" is visible across the system.
> +	 * Readers will see either a combination of before+disable
> +	 * state or disable+after.  They will never see before and
> +	 * after state together.
> +	 *
> +	 * The before+after state together might have cycles and
> +	 * could cause readers to do things like loop until this
> +	 * function finishes.  This ensures they can only see a
> +	 * single "bad" read and would, for instance, only loop
> +	 * once.
> +	 */
> +	smp_wmb();
> +
> +	/*
> +	 * Allocations go close to CPUs, first.  Assume that
> +	 * the migration path starts at the nodes with CPUs.
> +	 */
> +	next_pass = node_states[N_CPU];
> +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'.
> +	 *
> +	 * But, do this only once per pass so that multiple
> +	 * source nodes can share a target node.

establish_migrate_target() calls find_next_best_node(), which will set
target_node in used_targets.  So it seems that the nodes_or() below is
only necessary to initialize used_targets, and multiple source nodes
cannot share one target node in current implementation.

Best Regards,
Huang, Ying

> +	 */
> +	nodes_or(used_targets, used_targets, this_pass);
> +	for_each_node_mask(node, this_pass) {
> +		int target_node = establish_migrate_target(node, &used_targets);
> +
> +		if (target_node == NUMA_NO_NODE)
> +			continue;
> +
> +		/* Visit targets from this pass in the next pass: */
> +		node_set(target_node, next_pass);
> +	}
> +	/* Is another pass necessary? */
> +	if (!nodes_empty(next_pass))
> +		goto again;
> +
> +	put_online_mems();
> +}


  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 23:45 [RFC][PATCH 0/8] Migrate Pages in lieu of discard Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 1/8] mm/numa: node demotion data structure and lookup Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 2/8] mm/migrate: Defer allocating new page until needed Dave Hansen
2020-07-01  8:47   ` Greg Thelen
2020-07-01 14:46     ` Dave Hansen
2020-07-01 18:32       ` Yang Shi
2020-06-29 23:45 ` [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard Dave Hansen
2020-07-01  0:47   ` David Rientjes
2020-07-01  1:29     ` Yang Shi
2020-07-01  5:41       ` David Rientjes
2020-07-01  8:54         ` Huang, Ying
2020-07-01 18:20           ` Dave Hansen
2020-07-01 19:50             ` David Rientjes
2020-07-02  1:50               ` Huang, Ying
2020-07-01 15:15         ` Dave Hansen
2020-07-01 17:21         ` Yang Shi
2020-07-01 19:45           ` David Rientjes
2020-07-02 10:02             ` Jonathan Cameron
2020-07-01  1:40     ` Huang, Ying
2020-07-01 16:48     ` Dave Hansen
2020-07-01 19:25       ` David Rientjes
2020-07-02  5:02         ` Huang, Ying
2020-06-29 23:45 ` [RFC][PATCH 4/8] mm/vmscan: add page demotion counter Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 5/8] mm/numa: automatically generate node migration order Dave Hansen
2020-06-30  8:22   ` Huang, Ying [this message]
2020-07-01 18:23     ` Dave Hansen
2020-07-02  1:20       ` Huang, Ying
2020-06-29 23:45 ` [RFC][PATCH 6/8] mm/vmscan: Consider anonymous pages without swap Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 7/8] mm/vmscan: never demote for memcg reclaim Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 8/8] mm/numa: new reclaim mode to enable reclaim-based migration Dave Hansen
2020-06-30  7:23   ` Huang, Ying
2020-06-30 17:50     ` Yang Shi
2020-07-01  0:48       ` Huang, Ying
2020-07-01  1:12         ` Yang Shi
2020-07-01  1:28           ` Huang, Ying
2020-07-01 16:02       ` Dave Hansen
2020-07-03  9:30   ` Huang, Ying
2020-06-30 18:36 ` [RFC][PATCH 0/8] Migrate Pages in lieu of discard Shakeel Butt
2020-06-30 18:51   ` Dave Hansen
2020-06-30 19:25     ` Shakeel Butt
2020-06-30 19:31       ` Dave Hansen
2020-07-01 14:24         ` [RFC] [PATCH " Zi Yan
2020-07-01 14:32           ` Dave Hansen

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