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

From: Zhijian Li (Fujitsu)
Date: Thu Nov 02 2023 - 23:05:44 EST

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On 02/11/2023 13:58, Huang, Ying wrote:
> "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.

Very thanks for your kindly explanation. You are right.
Let me re-think if it's still needed...

BTW, i will split PATCH2 as a separate patch first.

Thanks
Zhijian

>
> --
> 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

Next message: Li Zhijian: "[PATCH v2] mm/vmstat: Move pgdemote_* to per-node stats"
Previous message: syzbot: "Re: [syzbot] [btrfs?] KASAN: slab-use-after-free Read in btrfs_qgroup_account_extent"
In reply to: Huang, Ying: "Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys infterface"
Next in thread: Li Zhijian: "[PATCH RFC 4/4] drivers/base/node: add demote_src and demote_dst to numastat"
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