mm/mempolicy: implement the sysfs-based weighted_interleave interface

Patch series "mm/mempolicy: weighted interleave mempolicy and sysfs
extension", v5.

Weighted interleave is a new interleave policy intended to make use of
heterogeneous memory environments appearing with CXL.

The existing interleave mechanism does an even round-robin distribution of
memory across all nodes in a nodemask, while weighted interleave
distributes memory across nodes according to a provided weight.  (Weight =
# of page allocations per round)

Weighted interleave is intended to reduce average latency when bandwidth
is pressured - therefore increasing total throughput.

In other words: It allows greater use of the total available bandwidth in
a heterogeneous hardware environment (different hardware provides
different bandwidth capacity).

As bandwidth is pressured, latency increases - first linearly and then
exponentially.  By keeping bandwidth usage distributed according to
available bandwidth, we therefore can reduce the average latency of a
cacheline fetch.

A good explanation of the bandwidth vs latency response curve:
https://mahmoudhatem.wordpress.com/2017/11/07/memory-bandwidth-vs-latency-response-curve/

From the article:
```
Constant region:
    The latency response is fairly constant for the first 40%
    of the sustained bandwidth.
Linear region:
    In between 40% to 80% of the sustained bandwidth, the
    latency response increases almost linearly with the bandwidth
    demand of the system due to contention overhead by numerous
    memory requests.
Exponential region:
    Between 80% to 100% of the sustained bandwidth, the memory
    latency is dominated by the contention latency which can be
    as much as twice the idle latency or more.
Maximum sustained bandwidth :
    Is 65% to 75% of the theoretical maximum bandwidth.
```

As a general rule of thumb:
* If bandwidth usage is low, latency does not increase. It is
  optimal to place data in the nearest (lowest latency) device.
* If bandwidth usage is high, latency increases. It is optimal
  to place data such that bandwidth use is optimized per-device.

This is the top line goal: Provide a user a mechanism to target using the
"maximum sustained bandwidth" of each hardware component in a heterogenous
memory system.


For example, the stream benchmark demonstrates that 1:1 (default)
interleave is actively harmful, while weighted interleave can be
beneficial.  Default interleave distributes data such that too much
pressure is placed on devices with lower available bandwidth.

Stream Benchmark (vs DRAM, 1 Socket + 1 CXL Device)
Default interleave : -78% (slower than DRAM)
Global weighting   : -6% to +4% (workload dependant)
Targeted weights   : +2.5% to +4% (consistently better than DRAM)

Global means the task-policy was set (set_mempolicy), while targeted means
VMA policies were set (mbind2).  We see weighted interleave is not always
beneficial when applied globally, but is always beneficial when applied to
bandwidth-driving memory regions.


There are 4 patches in this set:
1) Implement system-global interleave weights as sysfs extension
   in mm/mempolicy.c.  These weights are RCU protected, and a
   default weight set is provided (all weights are 1 by default).

   In future work, we intend to expose an interface for HMAT/CDAT
   code to set reasonable default values based on the memory
   configuration of the system discovered at boot/hotplug.

2) A mild refactor of some interleave-logic for re-use in the
   new weighted interleave logic.

3) MPOL_WEIGHTED_INTERLEAVE extension for set_mempolicy/mbind

4) Protect interleave logic (weighted and normal) with the
   mems_allowed seq cookie.  If the nodemask changes while
   accessing it during a rebind, just retry the access.

Included below are some performance and LTP test information,
and a sample numactl branch which can be used for testing.

= Performance summary =
(tests may have different configurations, see extended info below)
1) MLC (W2) : +38% over DRAM. +264% over default interleave.
   MLC (W5) : +40% over DRAM. +226% over default interleave.
2) Stream   : -6% to +4% over DRAM, +430% over default interleave.
3) XSBench  : +19% over DRAM. +47% over default interleave.

= LTP Testing Summary =
existing mempolicy & mbind tests: pass
mempolicy & mbind + weighted interleave (global weights): pass

= version history
v5:
- style fixes
- mems_allowed cookie protection to detect rebind issues,
  prevents spurious allocation failures and/or mis-allocations
- sparse warning fixes related to __rcu on local variables

=====================================================================
Performance tests - MLC
From - Ravi Jonnalagadda <ravis.opensrc@micron.com>

Hardware: Single-socket, multiple CXL memory expanders.

Workload:                               W2
Data Signature:                         2:1 read:write
DRAM only bandwidth (GBps):             298.8
DRAM + CXL (default interleave) (GBps): 113.04
DRAM + CXL (weighted interleave)(GBps): 412.5
Gain over DRAM only:                    1.38x
Gain over default interleave:           2.64x

Workload:                               W5
Data Signature:                         1:1 read:write
DRAM only bandwidth (GBps):             273.2
DRAM + CXL (default interleave) (GBps): 117.23
DRAM + CXL (weighted interleave)(GBps): 382.7
Gain over DRAM only:                    1.4x
Gain over default interleave:           2.26x

=====================================================================
Performance test - Stream
From - Gregory Price <gregory.price@memverge.com>

Hardware: Single socket, single CXL expander
numactl extension: https://github.com/gmprice/numactl/tree/weighted_interleave_master

Summary: 64 threads, ~18GB workload, 3GB per array, executed 100 times
Default interleave : -78% (slower than DRAM)
Global weighting   : -6% to +4% (workload dependant)
mbind2 weights     : +2.5% to +4% (consistently better than DRAM)

dram only:
numactl --cpunodebind=1 --membind=1 ./stream_c.exe --ntimes 100 --array-size 400M --malloc
Function     Direction    BestRateMBs     AvgTime      MinTime      MaxTime
Copy:        0->0            200923.2     0.032662     0.031853     0.033301
Scale:       0->0            202123.0     0.032526     0.031664     0.032970
Add:         0->0            208873.2     0.047322     0.045961     0.047884
Triad:       0->0            208523.8     0.047262     0.046038     0.048414

CXL-only:
numactl --cpunodebind=1 -w --membind=2 ./stream_c.exe --ntimes 100 --array-size 400M --malloc
Copy:        0->0             22209.7     0.288661     0.288162     0.289342
Scale:       0->0             22288.2     0.287549     0.287147     0.288291
Add:         0->0             24419.1     0.393372     0.393135     0.393735
Triad:       0->0             24484.6     0.392337     0.392083     0.394331

Based on the above, the optimal weights are ~9:1
echo 9 > /sys/kernel/mm/mempolicy/weighted_interleave/node1
echo 1 > /sys/kernel/mm/mempolicy/weighted_interleave/node2

default interleave:
numactl --cpunodebind=1 --interleave=1,2 ./stream_c.exe --ntimes 100 --array-size 400M --malloc
Copy:        0->0             44666.2     0.143671     0.143285     0.144174
Scale:       0->0             44781.6     0.143256     0.142916     0.143713
Add:         0->0             48600.7     0.197719     0.197528     0.197858
Triad:       0->0             48727.5     0.197204     0.197014     0.197439

global weighted interleave:
numactl --cpunodebind=1 -w --interleave=1,2 ./stream_c.exe --ntimes 100 --array-size 400M --malloc
Copy:        0->0            190085.9     0.034289     0.033669     0.034645
Scale:       0->0            207677.4     0.031909     0.030817     0.033061
Add:         0->0            202036.8     0.048737     0.047516     0.053409
Triad:       0->0            217671.5     0.045819     0.044103     0.046755

targted regions w/ global weights (modified stream to mbind2 malloc'd regions))
numactl --cpunodebind=1 --membind=1 ./stream_c.exe -b --ntimes 100 --array-size 400M --malloc
Copy:        0->0            205827.0     0.031445     0.031094     0.031984
Scale:       0->0            208171.8     0.031320     0.030744     0.032505
Add:         0->0            217352.0     0.045087     0.044168     0.046515
Triad:       0->0            216884.8     0.045062     0.044263     0.046982

=====================================================================
Performance tests - XSBench
From - Hyeongtak Ji <hyeongtak.ji@sk.com>

Hardware: Single socket, Single CXL memory Expander

NUMA node 0: 56 logical cores, 128 GB memory
NUMA node 2: 96 GB CXL memory
Threads:     56
Lookups:     170,000,000

Summary: +19% over DRAM. +47% over default interleave.

Performance tests - XSBench
1. dram only
$ numactl -m 0 ./XSBench -s XL –p 5000000
Runtime:     36.235 seconds
Lookups/s:   4,691,618

2. default interleave
$ numactl –i 0,2 ./XSBench –s XL –p 5000000
Runtime:     55.243 seconds
Lookups/s:   3,077,293

3. weighted interleave
numactl –w –i 0,2 ./XSBench –s XL –p 5000000
Runtime:     29.262 seconds
Lookups/s:   5,809,513

=====================================================================
LTP Tests: https://github.com/gmprice/ltp/tree/mempolicy2

= Existing tests
set_mempolicy, get_mempolicy, mbind

MPOL_WEIGHTED_INTERLEAVE added manually to test basic functionality but
did not adjust tests for weighting.  Basically the weights were set to 1,
which is the default, and it should behave the same as MPOL_INTERLEAVE if
logic is correct.

== set_mempolicy01 : passed   18, failed   0
== set_mempolicy02 : passed   10, failed   0
== set_mempolicy03 : passed   64, failed   0
== set_mempolicy04 : passed   32, failed   0
== set_mempolicy05 - n/a on non-x86
== set_mempolicy06 : passed   10, failed   0
   this is set_mempolicy02 + MPOL_WEIGHTED_INTERLEAVE
== set_mempolicy07 : passed   32, failed   0
   set_mempolicy04 + MPOL_WEIGHTED_INTERLEAVE
== get_mempolicy01 : passed   12, failed   0
   change: added MPOL_WEIGHTED_INTERLEAVE
== get_mempolicy02 : passed   2, failed   0
== mbind01 : passed   15, failed   0
   added MPOL_WEIGHTED_INTERLEAVE
== mbind02 : passed   4, failed   0
   added MPOL_WEIGHTED_INTERLEAVE
== mbind03 : passed   16, failed   0
   added MPOL_WEIGHTED_INTERLEAVE
== mbind04 : passed   48, failed   0
   added MPOL_WEIGHTED_INTERLEAVE

=====================================================================
numactl (set_mempolicy) w/ global weighting test
numactl fork: https://github.com/gmprice/numactl/tree/weighted_interleave_master

command: numactl -w --interleave=0,1 ./eatmem

result (weights 1:1):
0176a000 weighted interleave:0-1 heap anon=65793 dirty=65793 active=0 N0=32897 N1=32896 kernelpagesize_kB=4
7fceeb9ff000 weighted interleave:0-1 anon=65537 dirty=65537 active=0 N0=32768 N1=32769 kernelpagesize_kB=4
50% distribution is correct

result (weights 5:1):
01b14000 weighted interleave:0-1 heap anon=65793 dirty=65793 active=0 N0=54828 N1=10965 kernelpagesize_kB=4
7f47a1dff000 weighted interleave:0-1 anon=65537 dirty=65537 active=0 N0=54614 N1=10923 kernelpagesize_kB=4
16.666% distribution is correct

result (weights 1:5):
01f07000 weighted interleave:0-1 heap anon=65793 dirty=65793 active=0 N0=10966 N1=54827 kernelpagesize_kB=4
7f17b1dff000 weighted interleave:0-1 anon=65537 dirty=65537 active=0 N0=10923 N1=54614 kernelpagesize_kB=4
16.666% distribution is correct

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main (void)
{
        char* mem = malloc(1024*1024*256);
        memset(mem, 1, 1024*1024*256);
        for (int i = 0; i  < ((1024*1024*256)/4096); i++)
        {
                mem = malloc(4096);
                mem[0] = 1;
        }
        printf("done\n");
        getchar();
        return 0;
}


This patch (of 4):

This patch provides a way to set interleave weight information under sysfs
at /sys/kernel/mm/mempolicy/weighted_interleave/nodeN

The sysfs structure is designed as follows.

  $ tree /sys/kernel/mm/mempolicy/
  /sys/kernel/mm/mempolicy/ [1]
  └── weighted_interleave [2]
      ├── node0 [3]
      └── node1

Each file above can be explained as follows.

[1] mm/mempolicy: configuration interface for mempolicy subsystem

[2] weighted_interleave/: config interface for weighted interleave policy

[3] weighted_interleave/nodeN: weight for nodeN

If a node value is set to `0`, the system-default value will be used.
As of this patch, the system-default for all nodes is always 1.

Link: https://lkml.kernel.org/r/20240202170238.90004-1-gregory.price@memverge.com
Link: https://lkml.kernel.org/r/20240202170238.90004-2-gregory.price@memverge.com
Suggested-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Co-developed-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Co-developed-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
Signed-off-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Gregory Price <gourry.memverge@gmail.com>
Cc: Hasan Al Maruf <Hasan.Maruf@amd.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 223 insertions, 0 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5e519163c4dcb6..b4fccc921b6238 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -131,6 +131,32 @@ static struct mempolicy default_policy = {
 
 static struct mempolicy preferred_node_policy[MAX_NUMNODES];
 
+/*
+ * iw_table is the sysfs-set interleave weight table, a value of 0 denotes
+ * system-default value should be used. A NULL iw_table also denotes that
+ * system-default values should be used. Until the system-default table
+ * is implemented, the system-default is always 1.
+ *
+ * iw_table is RCU protected
+ */
+static u8 __rcu *iw_table;
+static DEFINE_MUTEX(iw_table_lock);
+
+static u8 get_il_weight(int node)
+{
+	u8 *table;
+	u8 weight;
+
+	rcu_read_lock();
+	table = rcu_dereference(iw_table);
+	/* if no iw_table, use system default */
+	weight = table ? table[node] : 1;
+	/* if value in iw_table is 0, use system default */
+	weight = weight ? weight : 1;
+	rcu_read_unlock();
+	return weight;
+}
+
 /**
  * numa_nearest_node - Find nearest node by state
  * @node: Node id to start the search
@@ -3063,3 +3089,200 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 		p += scnprintf(p, buffer + maxlen - p, ":%*pbl",
 			       nodemask_pr_args(&nodes));
 }
+
+#ifdef CONFIG_SYSFS
+struct iw_node_attr {
+	struct kobj_attribute kobj_attr;
+	int nid;
+};
+
+static ssize_t node_show(struct kobject *kobj, struct kobj_attribute *attr,
+			 char *buf)
+{
+	struct iw_node_attr *node_attr;
+	u8 weight;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+	weight = get_il_weight(node_attr->nid);
+	return sysfs_emit(buf, "%d\n", weight);
+}
+
+static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct iw_node_attr *node_attr;
+	u8 *new;
+	u8 *old;
+	u8 weight = 0;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+	if (count == 0 || sysfs_streq(buf, ""))
+		weight = 0;
+	else if (kstrtou8(buf, 0, &weight))
+		return -EINVAL;
+
+	new = kzalloc(nr_node_ids, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	mutex_lock(&iw_table_lock);
+	old = rcu_dereference_protected(iw_table,
+					lockdep_is_held(&iw_table_lock));
+	if (old)
+		memcpy(new, old, nr_node_ids);
+	new[node_attr->nid] = weight;
+	rcu_assign_pointer(iw_table, new);
+	mutex_unlock(&iw_table_lock);
+	synchronize_rcu();
+	kfree(old);
+	return count;
+}
+
+static struct iw_node_attr **node_attrs;
+
+static void sysfs_wi_node_release(struct iw_node_attr *node_attr,
+				  struct kobject *parent)
+{
+	if (!node_attr)
+		return;
+	sysfs_remove_file(parent, &node_attr->kobj_attr.attr);
+	kfree(node_attr->kobj_attr.attr.name);
+	kfree(node_attr);
+}
+
+static void sysfs_wi_release(struct kobject *wi_kobj)
+{
+	int i;
+
+	for (i = 0; i < nr_node_ids; i++)
+		sysfs_wi_node_release(node_attrs[i], wi_kobj);
+	kobject_put(wi_kobj);
+}
+
+static const struct kobj_type wi_ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
+	.release = sysfs_wi_release,
+};
+
+static int add_weight_node(int nid, struct kobject *wi_kobj)
+{
+	struct iw_node_attr *node_attr;
+	char *name;
+
+	node_attr = kzalloc(sizeof(*node_attr), GFP_KERNEL);
+	if (!node_attr)
+		return -ENOMEM;
+
+	name = kasprintf(GFP_KERNEL, "node%d", nid);
+	if (!name) {
+		kfree(node_attr);
+		return -ENOMEM;
+	}
+
+	sysfs_attr_init(&node_attr->kobj_attr.attr);
+	node_attr->kobj_attr.attr.name = name;
+	node_attr->kobj_attr.attr.mode = 0644;
+	node_attr->kobj_attr.show = node_show;
+	node_attr->kobj_attr.store = node_store;
+	node_attr->nid = nid;
+
+	if (sysfs_create_file(wi_kobj, &node_attr->kobj_attr.attr)) {
+		kfree(node_attr->kobj_attr.attr.name);
+		kfree(node_attr);
+		pr_err("failed to add attribute to weighted_interleave\n");
+		return -ENOMEM;
+	}
+
+	node_attrs[nid] = node_attr;
+	return 0;
+}
+
+static int add_weighted_interleave_group(struct kobject *root_kobj)
+{
+	struct kobject *wi_kobj;
+	int nid, err;
+
+	wi_kobj = kzalloc(sizeof(struct kobject), GFP_KERNEL);
+	if (!wi_kobj)
+		return -ENOMEM;
+
+	err = kobject_init_and_add(wi_kobj, &wi_ktype, root_kobj,
+				   "weighted_interleave");
+	if (err) {
+		kfree(wi_kobj);
+		return err;
+	}
+
+	for_each_node_state(nid, N_POSSIBLE) {
+		err = add_weight_node(nid, wi_kobj);
+		if (err) {
+			pr_err("failed to add sysfs [node%d]\n", nid);
+			break;
+		}
+	}
+	if (err)
+		kobject_put(wi_kobj);
+	return 0;
+}
+
+static void mempolicy_kobj_release(struct kobject *kobj)
+{
+	u8 *old;
+
+	mutex_lock(&iw_table_lock);
+	old = rcu_dereference_protected(iw_table,
+					lockdep_is_held(&iw_table_lock));
+	rcu_assign_pointer(iw_table, NULL);
+	mutex_unlock(&iw_table_lock);
+	synchronize_rcu();
+	kfree(old);
+	kfree(node_attrs);
+	kfree(kobj);
+}
+
+static const struct kobj_type mempolicy_ktype = {
+	.release = mempolicy_kobj_release
+};
+
+static int __init mempolicy_sysfs_init(void)
+{
+	int err;
+	static struct kobject *mempolicy_kobj;
+
+	mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
+	if (!mempolicy_kobj) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
+			     GFP_KERNEL);
+	if (!node_attrs) {
+		err = -ENOMEM;
+		goto mempol_out;
+	}
+
+	err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
+				   "mempolicy");
+	if (err)
+		goto node_out;
+
+	err = add_weighted_interleave_group(mempolicy_kobj);
+	if (err) {
+		pr_err("mempolicy sysfs structure failed to initialize\n");
+		kobject_put(mempolicy_kobj);
+		return err;
+	}
+
+	return err;
+node_out:
+	kfree(node_attrs);
+mempol_out:
+	kfree(mempolicy_kobj);
+err_out:
+	pr_err("failed to add mempolicy kobject to the system\n");
+	return err;
+}
+
+late_initcall(mempolicy_sysfs_init);
+#endif /* CONFIG_SYSFS */