linux-kernel - [PATCH -V8 01/10] mm/numa: node demotion data structure and lookup

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Message-Id: <20210618061537.434999-2-ying.huang@intel.com>
Date:   Fri, 18 Jun 2021 14:15:28 +0800
From:   Huang Ying <ying.huang@...el.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        Wei Xu <weixugc@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        osalvador <osalvador@...e.de>
Subject: [PATCH -V8 01/10] mm/numa: node demotion data structure and lookup

From: Dave Hansen <dave.hansen@...ux.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@...ux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Wei Xu <weixugc@...gle.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: osalvador <osalvador@...e.de>

--

changes since 20200122:
 * Make node_demotion[] __read_mostly

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.
---
 mm/migrate.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index b234c3f3acb7..6cab668132f9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1136,6 +1136,23 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	return rc;
 }
 
+static int node_demotion[MAX_NUMNODES] __read_mostly =
+	{[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.
-- 
2.30.2