Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys infterface

From: Huang, Ying
Date: Thu Nov 02 2023 - 02:00:45 EST

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In reply to: Zhijian Li (Fujitsu): "Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys infterface"
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"Zhijian Li (Fujitsu)" <lizhijian@xxxxxxxxxxx> writes:

> On 02/11/2023 13:18, Huang, Ying wrote:
>> "Zhijian Li (Fujitsu)" <lizhijian@xxxxxxxxxxx> writes:
>>
>>>> We have /sys/devices/virtual/memory_tiering/memory_tier*/nodelist
>>>> already. A node in a higher tier can demote to any node in the lower
>>>> tiers. What's more need to be displayed in nodeX/demotion_nodes?
>>>
>>> IIRC, they are not the same. memory_tier[number], where the number is shared by
>>> the memory using the same memory driver(dax/kmem etc). Not reflect the actual distance
>>> across nodes(different distance will be grouped into the same memory_tier).
>>> But demotion will only select the nearest nodelist to demote.
>>
>> In the following patchset, we will use the performance information from
>> HMAT to place nodes using the same memory driver into different memory
>> tiers.
>>
>> https://lore.kernel.org/all/20230926060628.265989-1-ying.huang@xxxxxxxxx/
>
> Thanks for your reminder. It seems like I've fallen behind the world by months.
> I will rebase on it later if this patch is still needed.
>
>>
>> The patch is in mm-stable tree.
>>
>>> Below is an example, node0 node1 are DRAM, node2 node3 are PMEM, but distance to DRAM nodes
>>> are different.
>>>
>>> # numactl -H
>>> available: 4 nodes (0-3)
>>> node 0 cpus: 0
>>> node 0 size: 964 MB
>>> node 0 free: 746 MB
>>> node 1 cpus: 1
>>> node 1 size: 685 MB
>>> node 1 free: 455 MB
>>> node 2 cpus:
>>> node 2 size: 896 MB
>>> node 2 free: 897 MB
>>> node 3 cpus:
>>> node 3 size: 896 MB
>>> node 3 free: 896 MB
>>> node distances:
>>> node 0 1 2 3
>>> 0: 10 20 20 25
>>> 1: 20 10 25 20
>>> 2: 20 25 10 20
>>> 3: 25 20 20 10
>>> # cat /sys/devices/system/node/node0/demotion_nodes
>>> 2
>>
>> node 2 is only the preferred demotion target. In fact, memory in node 0
>> can be demoted to node 2,3. Please check demote_folio_list() for
>> details.
>
> Have I missed something, at least the on master tree, nd->preferred only include the
> nearest ones(by specific algorithms), so in above numa topology, nd->preferred of
> node0 is node2 only. node0 distance to node3 is 25 greater than to node2(20).
>
>> 1657 int target_nid = next_demotion_node(pgdat->node_id);
>
> So target_nid cannot be node3 IIUC.
>
> (I cooked this patches weeks ago, maybe something has changed, i will also take a deep look later.)
>
> 1650 /*
> 1651 * Take folios on @demote_folios and attempt to demote them to another node.
> 1652 * Folios which are not demoted are left on @demote_folios.
> 1653 */
> 1654 static unsigned int demote_folio_list(struct list_head *demote_folios,
> 1655 struct pglist_data *pgdat)
> 1656 {
> 1657 int target_nid = next_demotion_node(pgdat->node_id);
> 1658 unsigned int nr_succeeded;
> 1659 nodemask_t allowed_mask;
> 1660
> 1661 struct migration_target_control mtc = {
> 1662 /*
> 1663 * Allocate from 'node', or fail quickly and quietly.
> 1664 * When this happens, 'page' will likely just be discarded
> 1665 * instead of migrated.
> 1666 */
> 1667 .gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | __GFP_NOWARN |
> 1668 __GFP_NOMEMALLOC | GFP_NOWAIT,
> 1669 .nid = target_nid,
> 1670 .nmask = &allowed_mask
> 1671 };
> 1672
> 1673 if (list_empty(demote_folios))
> 1674 return 0;
> 1675
> 1676 if (target_nid == NUMA_NO_NODE)
> 1677 return 0;
> 1678
> 1679 node_get_allowed_targets(pgdat, &allowed_mask);
> 1680
> 1681 /* Demotion ignores all cpuset and mempolicy settings */
> 1682 migrate_pages(demote_folios, alloc_demote_folio, NULL,
> 1683 (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
> 1684 &nr_succeeded);
>

In alloc_demote_folio(), target_nid is tried firstly. Then, if
allocation fails, any node in allowed_mask will be tried.

--
Best Regards,
Huang, Ying

>>
>>> # cat /sys/devices/system/node/node1/demotion_nodes
>>> 3
>>> # cat /sys/devices/virtual/memory_tiering/memory_tier22/nodelist
>>> 2-3
>>>
>>> Thanks
>>> Zhijian
>>>
>>> (I hate the outlook native reply composition format.)
>>> ________________________________________
>>> From: Huang, Ying <ying.huang@xxxxxxxxx>
>>> Sent: Thursday, November 2, 2023 11:17
>>> To: Li, Zhijian/李智坚
>>> Cc: Andrew Morton; Greg Kroah-Hartman; rafael@xxxxxxxxxx; linux-mm@xxxxxxxxx; Gotou, Yasunori/五島康文; linux-kernel@xxxxxxxxxxxxxxx
>>> Subject: Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys infterface
>>>
>>> Li Zhijian <lizhijian@xxxxxxxxxxx> writes:
>>>
>>>> It shows the demotion target nodes of a node. Export this information to
>>>> user directly.
>>>>
>>>> Below is an example where node0 node1 are DRAM, node3 is a PMEM node.
>>>> - Before PMEM is online, no demotion_nodes for node0 and node1.
>>>> $ cat /sys/devices/system/node/node0/demotion_nodes
>>>> <show nothing>
>>>> - After node3 is online as kmem
>>>> $ daxctl reconfigure-device --mode=system-ram --no-online dax0.0 && daxctl online-memory dax0.0
>>>> [
>>>> {
>>>> "chardev":"dax0.0",
>>>> "size":1054867456,
>>>> "target_node":3,
>>>> "align":2097152,
>>>> "mode":"system-ram",
>>>> "online_memblocks":0,
>>>> "total_memblocks":7
>>>> }
>>>> ]
>>>> $ cat /sys/devices/system/node/node0/demotion_nodes
>>>> 3
>>>> $ cat /sys/devices/system/node/node1/demotion_nodes
>>>> 3
>>>> $ cat /sys/devices/system/node/node3/demotion_nodes
>>>> <show nothing>
>>>
>>> We have /sys/devices/virtual/memory_tiering/memory_tier*/nodelist
>>> already. A node in a higher tier can demote to any node in the lower
>>> tiers. What's more need to be displayed in nodeX/demotion_nodes?
>>>
>>> --
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
>>>> ---
>>>> drivers/base/node.c | 13 +++++++++++++
>>>> include/linux/memory-tiers.h | 6 ++++++
>>>> mm/memory-tiers.c | 8 ++++++++
>>>> 3 files changed, 27 insertions(+)
>>>>
>>>> diff --git a/drivers/base/node.c b/drivers/base/node.c
>>>> index 493d533f8375..27e8502548a7 100644
>>>> --- a/drivers/base/node.c
>>>> +++ b/drivers/base/node.c
>>>> @@ -7,6 +7,7 @@
>>>> #include <linux/init.h>
>>>> #include <linux/mm.h>
>>>> #include <linux/memory.h>
>>>> +#include <linux/memory-tiers.h>
>>>> #include <linux/vmstat.h>
>>>> #include <linux/notifier.h>
>>>> #include <linux/node.h>
>>>> @@ -569,11 +570,23 @@ static ssize_t node_read_distance(struct device *dev,
>>>> }
>>>> static DEVICE_ATTR(distance, 0444, node_read_distance, NULL);
>>>>
>>>> +static ssize_t demotion_nodes_show(struct device *dev,
>>>> + struct device_attribute *attr, char *buf)
>>>> +{
>>>> + int ret;
>>>> + nodemask_t nmask = next_demotion_nodes(dev->id);
>>>> +
>>>> + ret = sysfs_emit(buf, "%*pbl\n", nodemask_pr_args(&nmask));
>>>> + return ret;
>>>> +}
>>>> +static DEVICE_ATTR_RO(demotion_nodes);
>>>> +
>>>> static struct attribute *node_dev_attrs[] = {
>>>> &dev_attr_meminfo.attr,
>>>> &dev_attr_numastat.attr,
>>>> &dev_attr_distance.attr,
>>>> &dev_attr_vmstat.attr,
>>>> + &dev_attr_demotion_nodes.attr,
>>>> NULL
>>>> };
>>>>
>>>> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
>>>> index 437441cdf78f..8eb04923f965 100644
>>>> --- a/include/linux/memory-tiers.h
>>>> +++ b/include/linux/memory-tiers.h
>>>> @@ -38,6 +38,7 @@ void init_node_memory_type(int node, struct memory_dev_type *default_type);
>>>> void clear_node_memory_type(int node, struct memory_dev_type *memtype);
>>>> #ifdef CONFIG_MIGRATION
>>>> int next_demotion_node(int node);
>>>> +nodemask_t next_demotion_nodes(int node);
>>>> void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
>>>> bool node_is_toptier(int node);
>>>> #else
>>>> @@ -46,6 +47,11 @@ static inline int next_demotion_node(int node)
>>>> return NUMA_NO_NODE;
>>>> }
>>>>
>>>> +static inline next_demotion_nodes next_demotion_nodes(int node)
>>>> +{
>>>> + return NODE_MASK_NONE;
>>>> +}
>>>> +
>>>> static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>>>> {
>>>> *targets = NODE_MASK_NONE;
>>>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>>>> index 37a4f59d9585..90047f37d98a 100644
>>>> --- a/mm/memory-tiers.c
>>>> +++ b/mm/memory-tiers.c
>>>> @@ -282,6 +282,14 @@ void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>>>> rcu_read_unlock();
>>>> }
>>>>
>>>> +nodemask_t next_demotion_nodes(int node)
>>>> +{
>>>> + if (!node_demotion)
>>>> + return NODE_MASK_NONE;
>>>> +
>>>> + return node_demotion[node].preferred;
>>>> +}
>>>> +
>>>> /**
>>>> * next_demotion_node() - Get the next node in the demotion path
>>>> * @node: The starting node to lookup the next node

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