[PATCH -V11 0/3] NUMA balancing: optimize memory placement for memory tiering system

[PATCH -V11 0/3] NUMA balancing: optimize memory placement for memory tiering system

[Huang Ying]

The changes since the last post are as follows,

- Rebased on v5.17-rc1

- Remove [4-6] from the original patchset to make it easier to be
  reviewed.

- Change the additional promotion watermark to be the high watermark / 4.

--

With the advent of various new memory types, some machines will have
multiple types of memory, e.g. DRAM and PMEM (persistent memory).  The
memory subsystem of these machines can be called memory tiering
system, because the performance of the different types of memory are
different.

After commit c221c0b0308f ("device-dax: "Hotplug" persistent memory
for use like normal RAM"), the PMEM could be used as the
cost-effective volatile memory in separate NUMA nodes.  In a typical
memory tiering system, there are CPUs, DRAM and PMEM in each physical
NUMA node.  The CPUs and the DRAM will be put in one logical node,
while the PMEM will be put in another (faked) logical node.

To optimize the system overall performance, the hot pages should be
placed in DRAM node.  To do that, we need to identify the hot pages in
the PMEM node and migrate them to DRAM node via NUMA migration.

In the original NUMA balancing, there are already a set of existing
mechanisms to identify the pages recently accessed by the CPUs in a
node and migrate the pages to the node.  So we can reuse these
mechanisms to build the mechanisms to optimize the page placement in
the memory tiering system.  This is implemented in this patchset.

At the other hand, the cold pages should be placed in PMEM node.  So,
we also need to identify the cold pages in the DRAM node and migrate
them to PMEM node.

In commit 26aa2d199d6f ("mm/migrate: demote pages during reclaim"), a
mechanism to demote the cold DRAM pages to PMEM node under memory
pressure is implemented.  Based on that, the cold DRAM pages can be
demoted to PMEM node proactively to free some memory space on DRAM
node to accommodate the promoted hot PMEM pages.  This is implemented
in this patchset too.

We have tested the solution with the pmbench memory accessing
benchmark with the 80:20 read/write ratio and the Gauss access address
distribution on a 2 socket Intel server with Optane DC Persistent
Memory Model.  The test results shows that the pmbench score can
improve up to 95.9%.

Changelog:

v11:

- Rebased on v5.17-rc1

- Remove [4-6] from the original patchset to make it easier to be
  reviewed.

- Change the additional promotion watermark to be the high watermark / 4.

v10:

- Rebased on v5.16-rc1

- Revise error processing for [1/6] (promotion counter) per Yang's comments

- Add sysctl document for [2/6] (optimize page placement)

- Reset threshold adjustment state when disable/enable tiering mode

- Reset threshold when workload transition is detected.

v9:

- Rebased on v5.15-rc4

- Make "add promotion counter" the first patch per Yang's comments

v8:

- Rebased on v5.15-rc1

- Make user-specified threshold take effect sooner

v7:

- Rebased on the mmots tree of 2021-07-15.

- Some minor fixes.

v6:

- Rebased on the latest page demotion patchset. (which bases on v5.11)

v5:

- Rebased on the latest page demotion patchset. (which bases on v5.10)

v4:

- Rebased on the latest page demotion patchset. (which bases on v5.9-rc6)

- Add page promotion counter.

v3:

- Move the rate limit control as late as possible per Mel Gorman's
  comments.

- Revise the hot page selection implementation to store page scan time
  in struct page.

- Code cleanup.

- Rebased on the latest page demotion patchset.

v2:

- Addressed comments for V1.

- Rebased on v5.5.

Best Regards,
Huang, Ying

[PATCH -V11 1/3] NUMA Balancing: add page promotion counter

[Huang Ying]

In a system with multiple memory types, e.g. DRAM and PMEM, the CPU
and DRAM in one socket will be put in one NUMA node as before, while
the PMEM will be put in another NUMA node as described in the
description of the commit c221c0b0308f ("device-dax: "Hotplug"
persistent memory for use like normal RAM").  So, the NUMA balancing
mechanism will identify all PMEM accesses as remote access and try to
promote the PMEM pages to DRAM.

To distinguish the number of the inter-type promoted pages from that
of the inter-socket migrated pages.  A new vmstat count is added.  The
counter is per-node (count in the target node).  So this can be used
to identify promotion imbalance among the NUMA nodes.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Wei Xu <weixugc@google.com>
Cc: osalvador <osalvador@suse.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 include/linux/mmzone.h |  3 +++
 include/linux/node.h   |  5 +++++
 mm/migrate.c           | 13 ++++++++++---
 mm/vmstat.c            |  3 +++
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index aed44e9b5d89..44bd054ca12b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -210,6 +210,9 @@ enum node_stat_item {
 	NR_PAGETABLE,		/* used for pagetables */
 #ifdef CONFIG_SWAP
 	NR_SWAPCACHE,
+#endif
+#ifdef CONFIG_NUMA_BALANCING
+	PGPROMOTE_SUCCESS,	/* promote successfully */
 #endif
 	NR_VM_NODE_STAT_ITEMS
 };
diff --git a/include/linux/node.h b/include/linux/node.h
index bb21fd631b16..81bbf1c0afd3 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -181,4 +181,9 @@ static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
 
 #define to_node(device) container_of(device, struct node, dev)
 
+static inline bool node_is_toptier(int node)
+{
+	return node_state(node, N_CPU);
+}
+
 #endif /* _LINUX_NODE_H_ */
diff --git a/mm/migrate.c b/mm/migrate.c
index 665dbe8cad72..a5971e9f6e6a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2072,6 +2072,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	pg_data_t *pgdat = NODE_DATA(node);
 	int isolated;
 	int nr_remaining;
+	int nr_succeeded;
 	LIST_HEAD(migratepages);
 	new_page_t *new;
 	bool compound;
@@ -2110,7 +2111,8 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 
 	list_add(&page->lru, &migratepages);
 	nr_remaining = migrate_pages(&migratepages, *new, NULL, node,
-				     MIGRATE_ASYNC, MR_NUMA_MISPLACED, NULL);
+				     MIGRATE_ASYNC, MR_NUMA_MISPLACED,
+				     &nr_succeeded);
 	if (nr_remaining) {
 		if (!list_empty(&migratepages)) {
 			list_del(&page->lru);
@@ -2119,8 +2121,13 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 			putback_lru_page(page);
 		}
 		isolated = 0;
-	} else
-		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_pages);
+	}
+	if (nr_succeeded) {
+		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
+		if (!node_is_toptier(page_to_nid(page)) && node_is_toptier(node))
+			mod_node_page_state(NODE_DATA(node), PGPROMOTE_SUCCESS,
+					    nr_succeeded);
+	}
 	BUG_ON(!list_empty(&migratepages));
 	return isolated;
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4057372745d0..846b670dd346 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1242,6 +1242,9 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_SWAP
 	"nr_swapcached",
 #endif
+#ifdef CONFIG_NUMA_BALANCING
+	"pgpromote_success",
+#endif
 
 	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",
-- 
2.30.2

[PATCH -V11 2/3] NUMA balancing: optimize page placement for memory tiering system

[Huang Ying]

With the advent of various new memory types, some machines will have
multiple types of memory, e.g. DRAM and PMEM (persistent memory).  The
memory subsystem of these machines can be called memory tiering
system, because the performance of the different types of memory are
usually different.

In such system, because of the memory accessing pattern changing etc,
some pages in the slow memory may become hot globally.  So in this
patch, the NUMA balancing mechanism is enhanced to optimize the page
placement among the different memory types according to hot/cold
dynamically.

In a typical memory tiering system, there are CPUs, fast memory and
slow memory in each physical NUMA node.  The CPUs and the fast memory
will be put in one logical node (called fast memory node), while the
slow memory will be put in another (faked) logical node (called slow
memory node).  That is, the fast memory is regarded as local while the
slow memory is regarded as remote.  So it's possible for the recently
accessed pages in the slow memory node to be promoted to the fast
memory node via the existing NUMA balancing mechanism.

The original NUMA balancing mechanism will stop to migrate pages if
the free memory of the target node becomes below the high watermark.
This is a reasonable policy if there's only one memory type.  But this
makes the original NUMA balancing mechanism almost do not work to
optimize page placement among different memory types.  Details are as
follows.

It's the common cases that the working-set size of the workload is
larger than the size of the fast memory nodes.  Otherwise, it's
unnecessary to use the slow memory at all.  So, there are almost
always no enough free pages in the fast memory nodes, so that the
globally hot pages in the slow memory node cannot be promoted to the
fast memory node.  To solve the issue, we have 2 choices as follows,

a. Ignore the free pages watermark checking when promoting hot pages
   from the slow memory node to the fast memory node.  This will
   create some memory pressure in the fast memory node, thus trigger
   the memory reclaiming.  So that, the cold pages in the fast memory
   node will be demoted to the slow memory node.

b. Make kswapd of the fast memory node to reclaim pages until the
   free pages are a little (for example, high_watermark / 4) more than
   the high watermark.  Then, if the free pages of the fast memory
   node reaches high watermark, and some hot pages need to be
   promoted, kswapd of the fast memory node will be waken up to demote
   more cold pages in the fast memory node to the slow memory node.
   This will free some extra space in the fast memory node, so the hot
   pages in the slow memory node can be promoted to the fast memory
   node.

The choice "a" may create high memory pressure in the fast memory
node.  If the memory pressure of the workload is high, the memory
pressure may become so high that the memory allocation latency of the
workload is influenced, e.g. the direct reclaiming may be triggered.

The choice "b" works much better at this aspect.  If the memory
pressure of the workload is high, the hot pages promotion will stop
earlier because its allocation watermark is higher than that of the
normal memory allocation.  So in this patch, choice "b" is
implemented.

In addition to the original page placement optimization among sockets,
the NUMA balancing mechanism is extended to be used to optimize page
placement according to hot/cold among different memory types.  So the
sysctl user space interface (numa_balancing) is extended in a backward
compatible way as follow, so that the users can enable/disable these
functionality individually.

The sysctl is converted from a Boolean value to a bits field.  The
definition of the flags is,

- 0x0: NUMA_BALANCING_DISABLED
- 0x1: NUMA_BALANCING_NORMAL
- 0x2: NUMA_BALANCING_MEMORY_TIERING

We have tested the patch with the pmbench memory accessing benchmark
with the 80:20 read/write ratio and the Gauss access address
distribution on a 2 socket Intel server with Optane DC Persistent
Memory Model.  The test results shows that the pmbench score can
improve up to 95.9%.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Wei Xu <weixugc@google.com>
Cc: osalvador <osalvador@suse.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 Documentation/admin-guide/sysctl/kernel.rst | 29 ++++++++++++++-------
 include/linux/sched/sysctl.h                | 10 +++++++
 kernel/sched/core.c                         | 21 ++++++++++++---
 kernel/sysctl.c                             |  2 +-
 mm/migrate.c                                | 19 ++++++++++++--
 mm/vmscan.c                                 | 17 ++++++++++++
 6 files changed, 82 insertions(+), 16 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index d359bcfadd39..ea32ba0c5d3c 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -595,16 +595,23 @@ Documentation/admin-guide/kernel-parameters.rst).
 numa_balancing
 ==============
 
-Enables/disables automatic page fault based NUMA memory
-balancing. Memory is moved automatically to nodes
-that access it often.
+Enables/disables and configure automatic page fault based NUMA memory
+balancing.  Memory is moved automatically to nodes that access it
+often.  The value to set can be the result to OR the following,
 
-Enables/disables automatic NUMA memory balancing. On NUMA machines, there
-is a performance penalty if remote memory is accessed by a CPU. When this
-feature is enabled the kernel samples what task thread is accessing memory
-by periodically unmapping pages and later trapping a page fault. At the
-time of the page fault, it is determined if the data being accessed should
-be migrated to a local memory node.
+= =================================
+0x0 NUMA_BALANCING_DISABLED
+0x1 NUMA_BALANCING_NORMAL
+0x2 NUMA_BALANCING_MEMORY_TIERING
+= =================================
+
+Or NUMA_BALANCING_NORMAL to optimize page placement among different
+NUMA nodes to reduce remote accessing.  On NUMA machines, there is a
+performance penalty if remote memory is accessed by a CPU. When this
+feature is enabled the kernel samples what task thread is accessing
+memory by periodically unmapping pages and later trapping a page
+fault. At the time of the page fault, it is determined if the data
+being accessed should be migrated to a local memory node.
 
 The unmapping of pages and trapping faults incur additional overhead that
 ideally is offset by improved memory locality but there is no universal
@@ -615,6 +622,10 @@ faults may be controlled by the `numa_balancing_scan_period_min_ms,
 numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
 numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
 
+Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
+different types of memory (represented as different NUMA nodes) to
+place the hot pages in the fast memory.  This is implemented based on
+unmapping and page fault too.
 
 numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
 ===============================================================================================================================
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index c19dd5a2c05c..b5eec8854c5a 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -23,6 +23,16 @@ enum sched_tunable_scaling {
 	SCHED_TUNABLESCALING_END,
 };
 
+#define NUMA_BALANCING_DISABLED		0x0
+#define NUMA_BALANCING_NORMAL		0x1
+#define NUMA_BALANCING_MEMORY_TIERING	0x2
+
+#ifdef CONFIG_NUMA_BALANCING
+extern int sysctl_numa_balancing_mode;
+#else
+#define sysctl_numa_balancing_mode	0
+#endif
+
 /*
  *  control realtime throttling:
  *
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 848eaa0efe0e..b8b8e5feb8ef 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4279,7 +4279,9 @@ DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
 
 #ifdef CONFIG_NUMA_BALANCING
 
-void set_numabalancing_state(bool enabled)
+int sysctl_numa_balancing_mode;
+
+static void __set_numabalancing_state(bool enabled)
 {
 	if (enabled)
 		static_branch_enable(&sched_numa_balancing);
@@ -4287,13 +4289,22 @@ void set_numabalancing_state(bool enabled)
 		static_branch_disable(&sched_numa_balancing);
 }
 
+void set_numabalancing_state(bool enabled)
+{
+	if (enabled)
+		sysctl_numa_balancing_mode = NUMA_BALANCING_NORMAL;
+	else
+		sysctl_numa_balancing_mode = NUMA_BALANCING_DISABLED;
+	__set_numabalancing_state(enabled);
+}
+
 #ifdef CONFIG_PROC_SYSCTL
 int sysctl_numa_balancing(struct ctl_table *table, int write,
 			  void *buffer, size_t *lenp, loff_t *ppos)
 {
 	struct ctl_table t;
 	int err;
-	int state = static_branch_likely(&sched_numa_balancing);
+	int state = sysctl_numa_balancing_mode;
 
 	if (write && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -4303,8 +4314,10 @@ int sysctl_numa_balancing(struct ctl_table *table, int write,
 	err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
 	if (err < 0)
 		return err;
-	if (write)
-		set_numabalancing_state(state);
+	if (write) {
+		sysctl_numa_balancing_mode = state;
+		__set_numabalancing_state(state);
+	}
 	return err;
 }
 #endif
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 5ae443b2882e..c90a564af720 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1689,7 +1689,7 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= sysctl_numa_balancing,
 		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.extra2		= SYSCTL_FOUR,
 	},
 #endif /* CONFIG_NUMA_BALANCING */
 	{
diff --git a/mm/migrate.c b/mm/migrate.c
index a5971e9f6e6a..61f7e82e6708 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -51,6 +51,7 @@
 #include <linux/oom.h>
 #include <linux/memory.h>
 #include <linux/random.h>
+#include <linux/sched/sysctl.h>
 
 #include <asm/tlbflush.h>
 
@@ -2034,16 +2035,30 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
 {
 	int page_lru;
 	int nr_pages = thp_nr_pages(page);
+	int order = compound_order(page);
 
-	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
+	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
 
 	/* Do not migrate THP mapped by multiple processes */
 	if (PageTransHuge(page) && total_mapcount(page) > 1)
 		return 0;
 
 	/* Avoid migrating to a node that is nearly full */
-	if (!migrate_balanced_pgdat(pgdat, nr_pages))
+	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
+		int z;
+
+		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
+		    !numa_demotion_enabled)
+			return 0;
+		if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
+			return 0;
+		for (z = pgdat->nr_zones - 1; z >= 0; z--) {
+			if (populated_zone(pgdat->node_zones + z))
+				break;
+		}
+		wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE);
 		return 0;
+	}
 
 	if (isolate_lru_page(page))
 		return 0;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 08ab556c7678..bc6fbbc8bedd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -56,6 +56,7 @@
 
 #include <linux/swapops.h>
 #include <linux/balloon_compaction.h>
+#include <linux/sched/sysctl.h>
 
 #include "internal.h"
 
@@ -3966,6 +3967,13 @@ static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
 	return false;
 }
 
+/*
+ * Keep the free pages on fast memory node a little more than the high
+ * watermark to accommodate the promoted pages.
+ */
+#define NUMA_BALANCING_PROMOTE_WATERMARK_DIV	4
+#define NUMA_BALANCING_PROMOTE_WATERMARK_MIN	(10UL * 1024 * 1024 >> PAGE_SHIFT)
+
 /*
  * Returns true if there is an eligible zone balanced for the request order
  * and highest_zoneidx
@@ -3987,6 +3995,15 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
 			continue;
 
 		mark = high_wmark_pages(zone);
+		if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
+		    numa_demotion_enabled &&
+		    next_demotion_node(pgdat->node_id) != NUMA_NO_NODE) {
+			unsigned long promote_mark;
+
+			promote_mark = max(NUMA_BALANCING_PROMOTE_WATERMARK_MIN,
+				mark / NUMA_BALANCING_PROMOTE_WATERMARK_DIV);
+			mark += promote_mark;
+		}
 		if (zone_watermark_ok_safe(zone, order, mark, highest_zoneidx))
 			return true;
 	}
-- 
2.30.2

[PATCH -V11 3/3] memory tiering: skip to scan fast memory

[Huang Ying]

If the NUMA balancing isn't used to optimize the page placement among
sockets but only among memory types, the hot pages in the fast memory
node couldn't be migrated (promoted) to anywhere.  So it's unnecessary
to scan the pages in the fast memory node via changing their PTE/PMD
mapping to be PROT_NONE.  So that the page faults could be avoided
too.

In the test, if only the memory tiering NUMA balancing mode is enabled, the
number of the NUMA balancing hint faults for the DRAM node is reduced to
almost 0 with the patch.  While the benchmark score doesn't change
visibly.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Wei Xu <weixugc@google.com>
Cc: osalvador <osalvador@suse.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 mm/huge_memory.c | 30 +++++++++++++++++++++---------
 mm/mprotect.c    | 13 ++++++++++++-
 2 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 406a3c28c026..9ce126cb0cfd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -34,6 +34,7 @@
 #include <linux/oom.h>
 #include <linux/numa.h>
 #include <linux/page_owner.h>
+#include <linux/sched/sysctl.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -1766,17 +1767,28 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 	}
 #endif
 
-	/*
-	 * Avoid trapping faults against the zero page. The read-only
-	 * data is likely to be read-cached on the local CPU and
-	 * local/remote hits to the zero page are not interesting.
-	 */
-	if (prot_numa && is_huge_zero_pmd(*pmd))
-		goto unlock;
+	if (prot_numa) {
+		struct page *page;
+		/*
+		 * Avoid trapping faults against the zero page. The read-only
+		 * data is likely to be read-cached on the local CPU and
+		 * local/remote hits to the zero page are not interesting.
+		 */
+		if (is_huge_zero_pmd(*pmd))
+			goto unlock;
 
-	if (prot_numa && pmd_protnone(*pmd))
-		goto unlock;
+		if (pmd_protnone(*pmd))
+			goto unlock;
 
+		page = pmd_page(*pmd);
+		/*
+		 * Skip scanning top tier node if normal numa
+		 * balancing is disabled
+		 */
+		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
+		    node_is_toptier(page_to_nid(page)))
+			goto unlock;
+	}
 	/*
 	 * In case prot_numa, we are under mmap_read_lock(mm). It's critical
 	 * to not clear pmd intermittently to avoid race with MADV_DONTNEED
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 0138dfcdb1d8..2fe03e695c81 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -29,6 +29,7 @@
 #include <linux/uaccess.h>
 #include <linux/mm_inline.h>
 #include <linux/pgtable.h>
+#include <linux/sched/sysctl.h>
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>
 #include <asm/tlbflush.h>
@@ -83,6 +84,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			 */
 			if (prot_numa) {
 				struct page *page;
+				int nid;
 
 				/* Avoid TLB flush if possible */
 				if (pte_protnone(oldpte))
@@ -109,7 +111,16 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 				 * Don't mess with PTEs if page is already on the node
 				 * a single-threaded process is running on.
 				 */
-				if (target_node == page_to_nid(page))
+				nid = page_to_nid(page);
+				if (target_node == nid)
+					continue;
+
+				/*
+				 * Skip scanning top tier node if normal numa
+				 * balancing is disabled
+				 */
+				if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
+				    node_is_toptier(nid))
 					continue;
 			}
 
-- 
2.30.2

Re: [PATCH -V11 1/3] NUMA Balancing: add page promotion counter

[Johannes Weiner]

On Fri, Jan 28, 2022 at 04:27:49PM +0800, Huang Ying wrote:
> In a system with multiple memory types, e.g. DRAM and PMEM, the CPU
> and DRAM in one socket will be put in one NUMA node as before, while
> the PMEM will be put in another NUMA node as described in the
> description of the commit c221c0b0308f ("device-dax: "Hotplug"
> persistent memory for use like normal RAM").  So, the NUMA balancing
> mechanism will identify all PMEM accesses as remote access and try to
> promote the PMEM pages to DRAM.
> 
> To distinguish the number of the inter-type promoted pages from that
> of the inter-socket migrated pages.  A new vmstat count is added.  The
> counter is per-node (count in the target node).  So this can be used
> to identify promotion imbalance among the NUMA nodes.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Yang Shi <shy828301@gmail.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: osalvador <osalvador@suse.de>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH -V11 2/3] NUMA balancing: optimize page placement for memory tiering system

[Johannes Weiner]

Hi Huang,

On Fri, Jan 28, 2022 at 04:27:50PM +0800, Huang Ying wrote:
> It's the common cases that the working-set size of the workload is
> larger than the size of the fast memory nodes.  Otherwise, it's
> unnecessary to use the slow memory at all.  So, there are almost
> always no enough free pages in the fast memory nodes, so that the
> globally hot pages in the slow memory node cannot be promoted to the
> fast memory node.  To solve the issue, we have 2 choices as follows,
> 
> a. Ignore the free pages watermark checking when promoting hot pages
>    from the slow memory node to the fast memory node.  This will
>    create some memory pressure in the fast memory node, thus trigger
>    the memory reclaiming.  So that, the cold pages in the fast memory
>    node will be demoted to the slow memory node.
> 
> b. Make kswapd of the fast memory node to reclaim pages until the
>    free pages are a little (for example, high_watermark / 4) more than
>    the high watermark.  Then, if the free pages of the fast memory
>    node reaches high watermark, and some hot pages need to be
>    promoted, kswapd of the fast memory node will be waken up to demote
>    more cold pages in the fast memory node to the slow memory node.
>    This will free some extra space in the fast memory node, so the hot
>    pages in the slow memory node can be promoted to the fast memory
>    node.
> 
> The choice "a" may create high memory pressure in the fast memory
> node.  If the memory pressure of the workload is high, the memory
> pressure may become so high that the memory allocation latency of the
> workload is influenced, e.g. the direct reclaiming may be triggered.
> 
> The choice "b" works much better at this aspect.  If the memory
> pressure of the workload is high, the hot pages promotion will stop
> earlier because its allocation watermark is higher than that of the
> normal memory allocation.  So in this patch, choice "b" is
> implemented.

I agree with that choice.

It's conceivable we'd eventually want a mix of both, where promotions
boost kswapd watermarks on-demand, such that no fast memory is wasted
if there are no references into slow memory. But that can be done when
it proves necessary, IMO.

> @@ -595,16 +595,23 @@ Documentation/admin-guide/kernel-parameters.rst).
>  numa_balancing
>  ==============
>  
> -Enables/disables automatic page fault based NUMA memory
> -balancing. Memory is moved automatically to nodes
> -that access it often.
> +Enables/disables and configure automatic page fault based NUMA memory
> +balancing.  Memory is moved automatically to nodes that access it
> +often.  The value to set can be the result to OR the following,
>  
> -Enables/disables automatic NUMA memory balancing. On NUMA machines, there
> -is a performance penalty if remote memory is accessed by a CPU. When this
> -feature is enabled the kernel samples what task thread is accessing memory
> -by periodically unmapping pages and later trapping a page fault. At the
> -time of the page fault, it is determined if the data being accessed should
> -be migrated to a local memory node.
> += =================================
> +0x0 NUMA_BALANCING_DISABLED
> +0x1 NUMA_BALANCING_NORMAL
> +0x2 NUMA_BALANCING_MEMORY_TIERING
> += =================================
> +
> +Or NUMA_BALANCING_NORMAL to optimize page placement among different
> +NUMA nodes to reduce remote accessing.  On NUMA machines, there is a
> +performance penalty if remote memory is accessed by a CPU. When this
> +feature is enabled the kernel samples what task thread is accessing
> +memory by periodically unmapping pages and later trapping a page
> +fault. At the time of the page fault, it is determined if the data
> +being accessed should be migrated to a local memory node.
>  
>  The unmapping of pages and trapping faults incur additional overhead that
>  ideally is offset by improved memory locality but there is no universal
> @@ -615,6 +622,10 @@ faults may be controlled by the `numa_balancing_scan_period_min_ms,
>  numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
>  numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
>  
> +Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
> +different types of memory (represented as different NUMA nodes) to
> +place the hot pages in the fast memory.  This is implemented based on
> +unmapping and page fault too.

NORMAL | TIERING appears to be a non-sensical combination.

Would it be better to have a tristate (disabled, normal, tiering)
rather than a mask?

> @@ -2034,16 +2035,30 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>  {
>  	int page_lru;
>  	int nr_pages = thp_nr_pages(page);
> +	int order = compound_order(page);
>  
> -	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
> +	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>  
>  	/* Do not migrate THP mapped by multiple processes */
>  	if (PageTransHuge(page) && total_mapcount(page) > 1)
>  		return 0;
>  
>  	/* Avoid migrating to a node that is nearly full */
> -	if (!migrate_balanced_pgdat(pgdat, nr_pages))
> +	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
> +		int z;
> +
> +		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
> +		    !numa_demotion_enabled)
> +			return 0;
> +		if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
> +			return 0;

The encoded behavior doesn't seem very user-friendly: Unless the user
enables numa demotion in a separate flag, enabling numa balancing in
tiered mode will silently do nothing.

Would it make more sense to have a central flag for the operation of
tiered memory systems that will enable both promotion and demotion?

Alternatively, it could also ignore the state of demotion and promote
anyway if asked to, resulting in regular reclaim to make room. It
might not be the most popular combination, but would be in line with
the zone_reclaim_mode policy of preferring reclaim over remote
accesses.  It would make the knobs behave more as expected and it's
less convoluted than having flags select other user-visible flags.

> @@ -3966,6 +3967,13 @@ static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
>  	return false;
>  }
>  
> +/*
> + * Keep the free pages on fast memory node a little more than the high
> + * watermark to accommodate the promoted pages.
> + */
> +#define NUMA_BALANCING_PROMOTE_WATERMARK_DIV	4
> +#define NUMA_BALANCING_PROMOTE_WATERMARK_MIN	(10UL * 1024 * 1024 >> PAGE_SHIFT)
> +
>  /*
>   * Returns true if there is an eligible zone balanced for the request order
>   * and highest_zoneidx
> @@ -3987,6 +3995,15 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
>  			continue;
>  
>  		mark = high_wmark_pages(zone);
> +		if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
> +		    numa_demotion_enabled &&
> +		    next_demotion_node(pgdat->node_id) != NUMA_NO_NODE) {
> +			unsigned long promote_mark;
> +
> +			promote_mark = max(NUMA_BALANCING_PROMOTE_WATERMARK_MIN,
> +				mark / NUMA_BALANCING_PROMOTE_WATERMARK_DIV);
> +			mark += promote_mark;
> +		}

I'm not sure about this formula.

The high watermark straddles both the atomic allocation pool
(min_free_kbytes) as well as the direct reclaim latency buffer
(watermark_scale_factor) on top of it. Making the promotion buffer a
quarter of the raw total number conflates the two settings.

E.g. if the user grows the atomic pool to support bursty network rx,
the two direct reclaim buffers between min, low and high stay the
same, but the tier-promotion buffer grows. This is unexpected, and not
what the user intended.

I'm thinking it would be better to do this:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7c417bec8207..5e067d66f797 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8573,7 +8573,8 @@ static void __setup_per_zone_wmarks(void)
 
 		zone->watermark_boost = 0;
 		zone->_watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
-		zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
+		zone->_watermark[WMARK_HIGH] = low_wmark_pages(zone) + tmp;
+		zone->_watermark[WMARK_PROMO] = high_wmark_pages(zone) + tmp;
 
 		spin_unlock_irqrestore(&zone->lock, flags);
 	}

and then have kswapd choose between the high and promo watermarks
depending on the numa balancing mode.

On my 32G desktop with default settings this produces the same
ballpark of values as your code - high/4=7424, tmp=7311.

This would behave more intuitively with the existing watermark tuning
knobs, and I think would make the code overall simpler as well.

Re: [PATCH -V11 3/3] memory tiering: skip to scan fast memory

[Johannes Weiner]

On Fri, Jan 28, 2022 at 04:27:51PM +0800, Huang Ying wrote:
> If the NUMA balancing isn't used to optimize the page placement among
> sockets but only among memory types, the hot pages in the fast memory
> node couldn't be migrated (promoted) to anywhere.  So it's unnecessary
> to scan the pages in the fast memory node via changing their PTE/PMD
> mapping to be PROT_NONE.  So that the page faults could be avoided
> too.
> 
> In the test, if only the memory tiering NUMA balancing mode is enabled, the
> number of the NUMA balancing hint faults for the DRAM node is reduced to
> almost 0 with the patch.  While the benchmark score doesn't change
> visibly.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: osalvador <osalvador@suse.de>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org

Looks good to me.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH -V11 2/3] NUMA balancing: optimize page placement for memory tiering system

[Huang, Ying]

Hi, Johannes,

Thanks a lot for your review!

Johannes Weiner <hannes@cmpxchg.org> writes:

> Hi Huang,
>
> On Fri, Jan 28, 2022 at 04:27:50PM +0800, Huang Ying wrote:
>> It's the common cases that the working-set size of the workload is
>> larger than the size of the fast memory nodes.  Otherwise, it's
>> unnecessary to use the slow memory at all.  So, there are almost
>> always no enough free pages in the fast memory nodes, so that the
>> globally hot pages in the slow memory node cannot be promoted to the
>> fast memory node.  To solve the issue, we have 2 choices as follows,
>> 
>> a. Ignore the free pages watermark checking when promoting hot pages
>>    from the slow memory node to the fast memory node.  This will
>>    create some memory pressure in the fast memory node, thus trigger
>>    the memory reclaiming.  So that, the cold pages in the fast memory
>>    node will be demoted to the slow memory node.
>> 
>> b. Make kswapd of the fast memory node to reclaim pages until the
>>    free pages are a little (for example, high_watermark / 4) more than
>>    the high watermark.  Then, if the free pages of the fast memory
>>    node reaches high watermark, and some hot pages need to be
>>    promoted, kswapd of the fast memory node will be waken up to demote
>>    more cold pages in the fast memory node to the slow memory node.
>>    This will free some extra space in the fast memory node, so the hot
>>    pages in the slow memory node can be promoted to the fast memory
>>    node.
>> 
>> The choice "a" may create high memory pressure in the fast memory
>> node.  If the memory pressure of the workload is high, the memory
>> pressure may become so high that the memory allocation latency of the
>> workload is influenced, e.g. the direct reclaiming may be triggered.
>> 
>> The choice "b" works much better at this aspect.  If the memory
>> pressure of the workload is high, the hot pages promotion will stop
>> earlier because its allocation watermark is higher than that of the
>> normal memory allocation.  So in this patch, choice "b" is
>> implemented.
>
> I agree with that choice.
>
> It's conceivable we'd eventually want a mix of both, where promotions
> boost kswapd watermarks on-demand, such that no fast memory is wasted
> if there are no references into slow memory. But that can be done when
> it proves necessary, IMO.

Sure.

>> @@ -595,16 +595,23 @@ Documentation/admin-guide/kernel-parameters.rst).
>>  numa_balancing
>>  ==============
>>  
>> -Enables/disables automatic page fault based NUMA memory
>> -balancing. Memory is moved automatically to nodes
>> -that access it often.
>> +Enables/disables and configure automatic page fault based NUMA memory
>> +balancing.  Memory is moved automatically to nodes that access it
>> +often.  The value to set can be the result to OR the following,
>>  
>> -Enables/disables automatic NUMA memory balancing. On NUMA machines, there
>> -is a performance penalty if remote memory is accessed by a CPU. When this
>> -feature is enabled the kernel samples what task thread is accessing memory
>> -by periodically unmapping pages and later trapping a page fault. At the
>> -time of the page fault, it is determined if the data being accessed should
>> -be migrated to a local memory node.
>> += =================================
>> +0x0 NUMA_BALANCING_DISABLED
>> +0x1 NUMA_BALANCING_NORMAL
>> +0x2 NUMA_BALANCING_MEMORY_TIERING
>> += =================================
>> +
>> +Or NUMA_BALANCING_NORMAL to optimize page placement among different
>> +NUMA nodes to reduce remote accessing.  On NUMA machines, there is a
>> +performance penalty if remote memory is accessed by a CPU. When this
>> +feature is enabled the kernel samples what task thread is accessing
>> +memory by periodically unmapping pages and later trapping a page
>> +fault. At the time of the page fault, it is determined if the data
>> +being accessed should be migrated to a local memory node.
>>  
>>  The unmapping of pages and trapping faults incur additional overhead that
>>  ideally is offset by improved memory locality but there is no universal
>> @@ -615,6 +622,10 @@ faults may be controlled by the `numa_balancing_scan_period_min_ms,
>>  numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
>>  numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
>>  
>> +Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
>> +different types of memory (represented as different NUMA nodes) to
>> +place the hot pages in the fast memory.  This is implemented based on
>> +unmapping and page fault too.
>
> NORMAL | TIERING appears to be a non-sensical combination.
>
> Would it be better to have a tristate (disabled, normal, tiering)
> rather than a mask?

NORMAL is for balancing cross-socket memory accessing among DRAM nodes.
TIERING is for optimizing page placement between DRAM and PMEM in one
socket.  We think it's possible to do both.

For example, with [3/3] of the patchset,

- TIERING: because DRAM pages aren't made PROT_NONE, it's disabled to
  balance among DRAM nodes.

- NORMAL | TIERING: both cross-socket balancing among DRAM nodes and
  page placement optimizing between DRAM and PMEM are enabled.

>> @@ -2034,16 +2035,30 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>>  {
>>  	int page_lru;
>>  	int nr_pages = thp_nr_pages(page);
>> +	int order = compound_order(page);
>>  
>> -	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
>> +	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>>  
>>  	/* Do not migrate THP mapped by multiple processes */
>>  	if (PageTransHuge(page) && total_mapcount(page) > 1)
>>  		return 0;
>>  
>>  	/* Avoid migrating to a node that is nearly full */
>> -	if (!migrate_balanced_pgdat(pgdat, nr_pages))
>> +	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
>> +		int z;
>> +
>> +		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
>> +		    !numa_demotion_enabled)
>> +			return 0;
>> +		if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
>> +			return 0;
>
> The encoded behavior doesn't seem very user-friendly: Unless the user
> enables numa demotion in a separate flag, enabling numa balancing in
> tiered mode will silently do nothing.

In theory, TIERING still does something even with numa_demotion_enabled
== false.  Where it works more like the original NUMA balancing.  If
there's some free space in DRAM node (for example, some programs exit),
some PMEM pages will be promoted to DRAM.  But as in the change log,
this isn't good enough for page placement optimizing.

> Would it make more sense to have a central flag for the operation of
> tiered memory systems that will enable both promotion and demotion?

IMHO, it may be possible for people to enable demotion alone.  For
example, if some people want to use a user space page placement
optimizing solution based on PMU counters, they may disable TIERING, but
still use demotion as a way to avoid swapping in some situation.  Do you
think this makes sense?

> Alternatively, it could also ignore the state of demotion and promote
> anyway if asked to, resulting in regular reclaim to make room. It
> might not be the most popular combination, but would be in line with
> the zone_reclaim_mode policy of preferring reclaim over remote
> accesses.  It would make the knobs behave more as expected and it's
> less convoluted than having flags select other user-visible flags.

Sorry, I don't get your idea here.  Do you suggest to add another knob
like zone_relcaim_mode?  Then we can define some bit to control demotion
and promotion there?  If so, I still don't know how to fit this into the
existing NUMA balancing framework.

>> @@ -3966,6 +3967,13 @@ static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
>>  	return false;
>>  }
>>  
>> +/*
>> + * Keep the free pages on fast memory node a little more than the high
>> + * watermark to accommodate the promoted pages.
>> + */
>> +#define NUMA_BALANCING_PROMOTE_WATERMARK_DIV	4
>> +#define NUMA_BALANCING_PROMOTE_WATERMARK_MIN	(10UL * 1024 * 1024 >> PAGE_SHIFT)
>> +
>>  /*
>>   * Returns true if there is an eligible zone balanced for the request order
>>   * and highest_zoneidx
>> @@ -3987,6 +3995,15 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
>>  			continue;
>>  
>>  		mark = high_wmark_pages(zone);
>> +		if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
>> +		    numa_demotion_enabled &&
>> +		    next_demotion_node(pgdat->node_id) != NUMA_NO_NODE) {
>> +			unsigned long promote_mark;
>> +
>> +			promote_mark = max(NUMA_BALANCING_PROMOTE_WATERMARK_MIN,
>> +				mark / NUMA_BALANCING_PROMOTE_WATERMARK_DIV);
>> +			mark += promote_mark;
>> +		}
>
> I'm not sure about this formula.
>
> The high watermark straddles both the atomic allocation pool
> (min_free_kbytes) as well as the direct reclaim latency buffer
> (watermark_scale_factor) on top of it. Making the promotion buffer a
> quarter of the raw total number conflates the two settings.
>
> E.g. if the user grows the atomic pool to support bursty network rx,
> the two direct reclaim buffers between min, low and high stay the
> same, but the tier-promotion buffer grows. This is unexpected, and not
> what the user intended.
>
> I'm thinking it would be better to do this:
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7c417bec8207..5e067d66f797 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8573,7 +8573,8 @@ static void __setup_per_zone_wmarks(void)
>  
>  		zone->watermark_boost = 0;
>  		zone->_watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
> -		zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
> +		zone->_watermark[WMARK_HIGH] = low_wmark_pages(zone) + tmp;
> +		zone->_watermark[WMARK_PROMO] = high_wmark_pages(zone) + tmp;
>  
>  		spin_unlock_irqrestore(&zone->lock, flags);
>  	}
>
> and then have kswapd choose between the high and promo watermarks
> depending on the numa balancing mode.
>
> On my 32G desktop with default settings this produces the same
> ballpark of values as your code - high/4=7424, tmp=7311.
>
> This would behave more intuitively with the existing watermark tuning
> knobs, and I think would make the code overall simpler as well.

Yes!  This looks great!  Will do this in the next version, Thanks!

Best Regards,
Huang, Ying

Re: [PATCH -V11 2/3] NUMA balancing: optimize page placement for memory tiering system

[Johannes Weiner]

Hi Huang,

Sorry, I didn't see this reply until you sent out the new version
already :( Apologies.

On Wed, Feb 09, 2022 at 01:24:29PM +0800, Huang, Ying wrote:
> > On Fri, Jan 28, 2022 at 04:27:50PM +0800, Huang Ying wrote:
> >> @@ -615,6 +622,10 @@ faults may be controlled by the `numa_balancing_scan_period_min_ms,
> >>  numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
> >>  numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
> >>  
> >> +Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
> >> +different types of memory (represented as different NUMA nodes) to
> >> +place the hot pages in the fast memory.  This is implemented based on
> >> +unmapping and page fault too.
> >
> > NORMAL | TIERING appears to be a non-sensical combination.
> >
> > Would it be better to have a tristate (disabled, normal, tiering)
> > rather than a mask?
> 
> NORMAL is for balancing cross-socket memory accessing among DRAM nodes.
> TIERING is for optimizing page placement between DRAM and PMEM in one
> socket.  We think it's possible to do both.
> 
> For example, with [3/3] of the patchset,
> 
> - TIERING: because DRAM pages aren't made PROT_NONE, it's disabled to
>   balance among DRAM nodes.
> 
> - NORMAL | TIERING: both cross-socket balancing among DRAM nodes and
>   page placement optimizing between DRAM and PMEM are enabled.

Ok, I get it. So NORMAL would enable PROT_NONE sampling on all nodes,
and TIERING would additionally raise the watermarks on DRAM nodes.

Thanks!

> >> @@ -2034,16 +2035,30 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> >>  {
> >>  	int page_lru;
> >>  	int nr_pages = thp_nr_pages(page);
> >> +	int order = compound_order(page);
> >>  
> >> -	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
> >> +	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
> >>  
> >>  	/* Do not migrate THP mapped by multiple processes */
> >>  	if (PageTransHuge(page) && total_mapcount(page) > 1)
> >>  		return 0;
> >>  
> >>  	/* Avoid migrating to a node that is nearly full */
> >> -	if (!migrate_balanced_pgdat(pgdat, nr_pages))
> >> +	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
> >> +		int z;
> >> +
> >> +		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
> >> +		    !numa_demotion_enabled)
> >> +			return 0;
> >> +		if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
> >> +			return 0;
> >
> > The encoded behavior doesn't seem very user-friendly: Unless the user
> > enables numa demotion in a separate flag, enabling numa balancing in
> > tiered mode will silently do nothing.
> 
> In theory, TIERING still does something even with numa_demotion_enabled
> == false.  Where it works more like the original NUMA balancing.  If
> there's some free space in DRAM node (for example, some programs exit),
> some PMEM pages will be promoted to DRAM.  But as in the change log,
> this isn't good enough for page placement optimizing.

Right, so it's a behavior that likely isn't going to be useful.

> > Would it make more sense to have a central flag for the operation of
> > tiered memory systems that will enable both promotion and demotion?
> 
> IMHO, it may be possible for people to enable demotion alone.  For
> example, if some people want to use a user space page placement
> optimizing solution based on PMU counters, they may disable TIERING, but
> still use demotion as a way to avoid swapping in some situation.  Do you
> think this makes sense?

Yes, it does.

> > Alternatively, it could also ignore the state of demotion and promote
> > anyway if asked to, resulting in regular reclaim to make room. It
> > might not be the most popular combination, but would be in line with
> > the zone_reclaim_mode policy of preferring reclaim over remote
> > accesses.  It would make the knobs behave more as expected and it's
> > less convoluted than having flags select other user-visible flags.
> 
> Sorry, I don't get your idea here.  Do you suggest to add another knob
> like zone_relcaim_mode?  Then we can define some bit to control demotion
> and promotion there?  If so, I still don't know how to fit this into the
> existing NUMA balancing framework.

No, I'm just suggesting to remove the !numa_demotion_disabled check
from the promotion path on unbalanced nodes. Keep the switches
independent from each other.

Like you said, demotion without promotion can be a valid config with a
userspace promoter.

And I'm saying promotion without demotion can be a valid config in a
zone_reclaim_mode type of setup.

We also seem to agree degraded promotion when demotion enabled likely
isn't very useful to anybody. So maybe it should be removed?

It just comes down to user expectations. There is no masterswitch that
says "do the right thing on tiered systems", so absent of that I think
it would be best to keep the semantics of each of the two knobs simple
and predictable, without tricky interdependencies - like quietly
degrading promotion behavior when demotion is disabled.

Does that make sense?

Thanks!
Johannes

Re: [PATCH -V11 2/3] NUMA balancing: optimize page placement for memory tiering system

[Huang, Ying]

Johannes Weiner <hannes@cmpxchg.org> writes:

> Hi Huang,
>
> Sorry, I didn't see this reply until you sent out the new version
> already :( Apologies.

Never mind!

> On Wed, Feb 09, 2022 at 01:24:29PM +0800, Huang, Ying wrote:
>> > On Fri, Jan 28, 2022 at 04:27:50PM +0800, Huang Ying wrote:
>> >> @@ -615,6 +622,10 @@ faults may be controlled by the `numa_balancing_scan_period_min_ms,
>> >>  numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
>> >>  numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
>> >>  
>> >> +Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
>> >> +different types of memory (represented as different NUMA nodes) to
>> >> +place the hot pages in the fast memory.  This is implemented based on
>> >> +unmapping and page fault too.
>> >
>> > NORMAL | TIERING appears to be a non-sensical combination.
>> >
>> > Would it be better to have a tristate (disabled, normal, tiering)
>> > rather than a mask?
>> 
>> NORMAL is for balancing cross-socket memory accessing among DRAM nodes.
>> TIERING is for optimizing page placement between DRAM and PMEM in one
>> socket.  We think it's possible to do both.
>> 
>> For example, with [3/3] of the patchset,
>> 
>> - TIERING: because DRAM pages aren't made PROT_NONE, it's disabled to
>>   balance among DRAM nodes.
>> 
>> - NORMAL | TIERING: both cross-socket balancing among DRAM nodes and
>>   page placement optimizing between DRAM and PMEM are enabled.
>
> Ok, I get it. So NORMAL would enable PROT_NONE sampling on all nodes,
> and TIERING would additionally raise the watermarks on DRAM nodes.
>
> Thanks!
>
>> >> @@ -2034,16 +2035,30 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>> >>  {
>> >>  	int page_lru;
>> >>  	int nr_pages = thp_nr_pages(page);
>> >> +	int order = compound_order(page);
>> >>  
>> >> -	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
>> >> +	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>> >>  
>> >>  	/* Do not migrate THP mapped by multiple processes */
>> >>  	if (PageTransHuge(page) && total_mapcount(page) > 1)
>> >>  		return 0;
>> >>  
>> >>  	/* Avoid migrating to a node that is nearly full */
>> >> -	if (!migrate_balanced_pgdat(pgdat, nr_pages))
>> >> +	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
>> >> +		int z;
>> >> +
>> >> +		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
>> >> +		    !numa_demotion_enabled)
>> >> +			return 0;
>> >> +		if (next_demotion_node(pgdat->node_id) == NUMA_NO_NODE)
>> >> +			return 0;
>> >
>> > The encoded behavior doesn't seem very user-friendly: Unless the user
>> > enables numa demotion in a separate flag, enabling numa balancing in
>> > tiered mode will silently do nothing.
>> 
>> In theory, TIERING still does something even with numa_demotion_enabled
>> == false.  Where it works more like the original NUMA balancing.  If
>> there's some free space in DRAM node (for example, some programs exit),
>> some PMEM pages will be promoted to DRAM.  But as in the change log,
>> this isn't good enough for page placement optimizing.
>
> Right, so it's a behavior that likely isn't going to be useful.
>
>> > Would it make more sense to have a central flag for the operation of
>> > tiered memory systems that will enable both promotion and demotion?
>> 
>> IMHO, it may be possible for people to enable demotion alone.  For
>> example, if some people want to use a user space page placement
>> optimizing solution based on PMU counters, they may disable TIERING, but
>> still use demotion as a way to avoid swapping in some situation.  Do you
>> think this makes sense?
>
> Yes, it does.
>
>> > Alternatively, it could also ignore the state of demotion and promote
>> > anyway if asked to, resulting in regular reclaim to make room. It
>> > might not be the most popular combination, but would be in line with
>> > the zone_reclaim_mode policy of preferring reclaim over remote
>> > accesses.  It would make the knobs behave more as expected and it's
>> > less convoluted than having flags select other user-visible flags.
>> 
>> Sorry, I don't get your idea here.  Do you suggest to add another knob
>> like zone_relcaim_mode?  Then we can define some bit to control demotion
>> and promotion there?  If so, I still don't know how to fit this into the
>> existing NUMA balancing framework.
>
> No, I'm just suggesting to remove the !numa_demotion_disabled check
> from the promotion path on unbalanced nodes. Keep the switches
> independent from each other.
>
> Like you said, demotion without promotion can be a valid config with a
> userspace promoter.
>
> And I'm saying promotion without demotion can be a valid config in a
> zone_reclaim_mode type of setup.
>
> We also seem to agree degraded promotion when demotion enabled likely
> isn't very useful to anybody. So maybe it should be removed?
>
> It just comes down to user expectations. There is no masterswitch that
> says "do the right thing on tiered systems", so absent of that I think
> it would be best to keep the semantics of each of the two knobs simple
> and predictable, without tricky interdependencies - like quietly
> degrading promotion behavior when demotion is disabled.
>
> Does that make sense?

Yes.  It does.  I will do that in the next version!

Best Regards,
Huang, Ying