diff mbox series

[RFC,04/13] mm/numa: node demotion data structure and lookup

Message ID 20210126003419.43281680@viggo.jf.intel.com (mailing list archive)
State New, archived
Headers show
Series Migrate Pages in lieu of discard | expand

Commit Message

Dave Hansen Jan. 26, 2021, 12:34 a.m. UTC 
From: Dave Hansen <dave.hansen@linux.intel.com>

Prepare for the kernel to auto-migrate pages to other memory nodes
with a user defined node migration table. This allows creating single
migration target for each NUMA node to enable the kernel to do NUMA
page migrations instead of simply reclaiming colder pages. A node
with no target is a "terminal node", so reclaim acts normally there.
The migration target does not fundamentally _need_ to be a single node,
but this implementation starts there to limit complexity.

If you consider the migration path as a graph, cycles (loops) in the
graph are disallowed.  This avoids wasting resources by constantly
migrating (A->B, B->A, A->B ...).  The expectation is that cycles will
never be allowed.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: osalvador <osalvador@suse.de>

--

changes in July 2020:
 - Remove loop from next_demotion_node() and get_online_mems().
   This means that the node returned by next_demotion_node()
   might now be offline, but the worst case is that the
   allocation fails.  That's fine since it is transient.
---

 b/mm/migrate.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Comments

David Rientjes Jan. 31, 2021, 1:19 a.m. UTC | #1 
On Mon, 25 Jan 2021, Dave Hansen wrote:

> diff -puN mm/migrate.c~0006-node-Define-and-export-memory-migration-path mm/migrate.c
> --- a/mm/migrate.c~0006-node-Define-and-export-memory-migration-path	2021-01-25 16:23:09.553866709 -0800
> +++ b/mm/migrate.c	2021-01-25 16:23:09.558866709 -0800
> @@ -1161,6 +1161,22 @@ out:
>  	return rc;
>  }
>  
> +static int node_demotion[MAX_NUMNODES] = {[0 ...  MAX_NUMNODES - 1] = NUMA_NO_NODE};

__read_mostly?

> +
> +/**
> + * next_demotion_node() - Get the next node in the demotion path
> + * @node: The starting node to lookup the next node
> + *
> + * @returns: node id for next memory node in the demotion path hierarchy
> + * from @node; NUMA_NO_NODE if @node is terminal.  This does not keep
> + * @node online or guarantee that it *continues* to be the next demotion
> + * target.
> + */
> +int next_demotion_node(int node)
> +{
> +	return node_demotion[node];
> +}
> +
>  /*
>   * Obtain the lock on page, remove all ptes and migrate the page
>   * to the newly allocated page in newpage.
> _
>
Dave Hansen Feb. 1, 2021, 5:49 p.m. UTC | #2 
On 1/30/21 5:19 PM, David Rientjes wrote:
> On Mon, 25 Jan 2021, Dave Hansen wrote:
> 
>> diff -puN mm/migrate.c~0006-node-Define-and-export-memory-migration-path mm/migrate.c
>> --- a/mm/migrate.c~0006-node-Define-and-export-memory-migration-path	2021-01-25 16:23:09.553866709 -0800
>> +++ b/mm/migrate.c	2021-01-25 16:23:09.558866709 -0800
>> @@ -1161,6 +1161,22 @@ out:
>>  	return rc;
>>  }
>>  
>> +static int node_demotion[MAX_NUMNODES] = {[0 ...  MAX_NUMNODES - 1] = NUMA_NO_NODE};
> 
> __read_mostly?

Yep, that's sane.  I'll fix that up in the next revision.
diff mbox series

Patch

diff -puN mm/migrate.c~0006-node-Define-and-export-memory-migration-path mm/migrate.c
--- a/mm/migrate.c~0006-node-Define-and-export-memory-migration-path	2021-01-25 16:23:09.553866709 -0800
+++ b/mm/migrate.c	2021-01-25 16:23:09.558866709 -0800
@@ -1161,6 +1161,22 @@  out:
 	return rc;
 }
 
+static int node_demotion[MAX_NUMNODES] = {[0 ...  MAX_NUMNODES - 1] = NUMA_NO_NODE};
+
+/**
+ * next_demotion_node() - Get the next node in the demotion path
+ * @node: The starting node to lookup the next node
+ *
+ * @returns: node id for next memory node in the demotion path hierarchy
+ * from @node; NUMA_NO_NODE if @node is terminal.  This does not keep
+ * @node online or guarantee that it *continues* to be the next demotion
+ * target.
+ */
+int next_demotion_node(int node)
+{
+	return node_demotion[node];
+}
+
 /*
  * Obtain the lock on page, remove all ptes and migrate the page
  * to the newly allocated page in newpage.