[PATCH v3 0/2] handle memoryless nodes more appropriately

[PATCH v3 0/2] handle memoryless nodes more appropriately

[Qi Zheng]

Hi all,

Currently, in the process of initialization or offline memory, memoryless
nodes will still be built into the fallback list of itself or other nodes.

This is not what we expected, so this patch series removes memoryless
nodes from the fallback list entirely.

This series is based on the next-20231018.

Comments and suggestions are welcome.

Thanks,
Qi

Changlog in v2 -> v3:
 - add a comment in [PATCH v2 2/2] (suggested by David Hildenbrand)
 - collect Acked-bys

Changlog in v1 -> v2:
 - modify the commit message in [PATCH 1/2], mention that it can also fix the
   specific crash. (suggested by Ingo Molnar)
 - rebase onto the next-20231018

Qi Zheng (2):
  mm: page_alloc: skip memoryless nodes entirely
  mm: memory_hotplug: drop memoryless node from fallback lists

 mm/memory_hotplug.c | 6 +++++-
 mm/page_alloc.c     | 7 +++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

-- 
2.30.2

[PATCH v3 1/2] mm: page_alloc: skip memoryless nodes entirely

[Qi Zheng]

In find_next_best_node(), We skipped the memoryless nodes
when building the zonelists of other normal nodes (N_NORMAL),
but did not skip the memoryless node itself when building
the zonelist. This will cause it to be traversed at runtime.

For example, say we have node0 and node1, node0 is memoryless
node, then the fallback order of node0 and node1 as follows:

[    0.153005] Fallback order for Node 0: 0 1
[    0.153564] Fallback order for Node 1: 1

After this patch, we skip memoryless node0 entirely, then
the fallback order of node0 and node1 as follows:

[    0.155236] Fallback order for Node 0: 1
[    0.155806] Fallback order for Node 1: 1

So it becomes completely invisible, which will reduce runtime
overhead.

And in this way, we will not try to allocate pages from memoryless
node0, then the panic mentioned in [1] will also be fixed. Even though
this problem has been solved by dropping the NODE_MIN_SIZE constrain
in x86 [2], it would be better to fix it in core MM as well.

[1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
[2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ee392a324802..e978272699d3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5052,8 +5052,11 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
 	int min_val = INT_MAX;
 	int best_node = NUMA_NO_NODE;
 
-	/* Use the local node if we haven't already */
-	if (!node_isset(node, *used_node_mask)) {
+	/*
+	 * Use the local node if we haven't already. But for memoryless local
+	 * node, we should skip it and fallback to other nodes.
+	 */
+	if (!node_isset(node, *used_node_mask) && node_state(node, N_MEMORY)) {
 		node_set(node, *used_node_mask);
 		return node;
 	}
-- 
2.30.2

[PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Qi Zheng]

In offline_pages(), if a node becomes memoryless, we
will clear its N_MEMORY state by calling node_states_clear_node().
But we do this after rebuilding the zonelists by calling
build_all_zonelists(), which will cause this memoryless node to
still be in the fallback list of other nodes. This will incur
some runtime overhead.

To drop memoryless node from fallback lists in this case, just
call node_states_clear_node() before calling build_all_zonelists().

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index d4a364fdaf8f..f019f7d6272c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -2036,12 +2036,16 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 	/* reinitialise watermarks and update pcp limits */
 	init_per_zone_wmark_min();
 
+	/*
+	 * Make sure to mark the node as memory-less before rebuilding the zone
+	 * list. Otherwise this node would still appear in the fallback lists.
+	 */
+	node_states_clear_node(node, &arg);
 	if (!populated_zone(zone)) {
 		zone_pcp_reset(zone);
 		build_all_zonelists(NULL);
 	}
 
-	node_states_clear_node(node, &arg);
 	if (arg.status_change_nid >= 0) {
 		kcompactd_stop(node);
 		kswapd_stop(node);
-- 
2.30.2

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Huang, Ying]

Qi Zheng <zhengqi.arch@bytedance.com> writes:

> In offline_pages(), if a node becomes memoryless, we
> will clear its N_MEMORY state by calling node_states_clear_node().
> But we do this after rebuilding the zonelists by calling
> build_all_zonelists(), which will cause this memoryless node to
> still be in the fallback list of other nodes.

For fallback list, do you mean pgdat->node_zonelists[]?  If so, in

build_all_zonelists
  __build_all_zonelists
    build_zonelists
      build_zonelists_in_node_order
        build_zonerefs_node

populated_zone() will be checked before adding zone into zonelist.

So, IIUC, we will not try to allocate from the memory less node.

--
Best Regards,
Huang, Ying


> This will incur
> some runtime overhead.
>
> To drop memoryless node from fallback lists in this case, just
> call node_states_clear_node() before calling build_all_zonelists().
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: David Hildenbrand <david@redhat.com>

[snip]

--
Best Regards,
Huang, Ying

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Qi Zheng]

Hi Ying,

On 2023/10/20 15:05, Huang, Ying wrote:
> Qi Zheng <zhengqi.arch@bytedance.com> writes:
> 
>> In offline_pages(), if a node becomes memoryless, we
>> will clear its N_MEMORY state by calling node_states_clear_node().
>> But we do this after rebuilding the zonelists by calling
>> build_all_zonelists(), which will cause this memoryless node to
>> still be in the fallback list of other nodes.
> 
> For fallback list, do you mean pgdat->node_zonelists[]?  If so, in
> 
> build_all_zonelists
>    __build_all_zonelists
>      build_zonelists
>        build_zonelists_in_node_order
>          build_zonerefs_node
> 
> populated_zone() will be checked before adding zone into zonelist.
> 
> So, IIUC, we will not try to allocate from the memory less node.

Normally yes, but if it is the weird topology mentioned in [1], it's
possible to allocate memory from it, it is a memoryless node, but it
also has memory.

In addition to the above case, I think it's reasonable to remove
memory less node from node_order[] in advance. In this way it will
not to be traversed in build_zonelists_in_node_order().

[1]. 
https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/

Thanks,
Qi


> 
> --
> Best Regards,
> Huang, Ying
> 
> 
>> This will incur
>> some runtime overhead.
>>
>> To drop memoryless node from fallback lists in this case, just
>> call node_states_clear_node() before calling build_all_zonelists().
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
> 
> [snip]
> 
> --
> Best Regards,
> Huang, Ying

Re: [PATCH v3 1/2] mm: page_alloc: skip memoryless nodes entirely

[Ingo Molnar]

* Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> In find_next_best_node(), We skipped the memoryless nodes

s/We
 /we

s/the memoryless nodes
 /memoryless nodes

> when building the zonelists of other normal nodes (N_NORMAL),
> but did not skip the memoryless node itself when building
> the zonelist. This will cause it to be traversed at runtime.
> 
> For example, say we have node0 and node1, node0 is memoryless
> node, then the fallback order of node0 and node1 as follows:
> 
> [    0.153005] Fallback order for Node 0: 0 1
> [    0.153564] Fallback order for Node 1: 1
> 
> After this patch, we skip memoryless node0 entirely, then
> the fallback order of node0 and node1 as follows:

s/fallback
 /fall back

> 
> [    0.155236] Fallback order for Node 0: 1
> [    0.155806] Fallback order for Node 1: 1
> 
> So it becomes completely invisible, which will reduce runtime
> overhead.
> 
> And in this way, we will not try to allocate pages from memoryless
> node0, then the panic mentioned in [1] will also be fixed. Even though
> this problem has been solved by dropping the NODE_MIN_SIZE constrain
> in x86 [2], it would be better to fix it in core MM as well.

s/in core MM
 /in the core MM

> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
> [2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: David Hildenbrand <david@redhat.com>

> +	/*
> +	 * Use the local node if we haven't already. But for memoryless local
> +	 * node, we should skip it and fallback to other nodes.

s/fallback
 /fall back

s/already. But
 /already, but

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Ingo Molnar]

* Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> In offline_pages(), if a node becomes memoryless, we
> will clear its N_MEMORY state by calling node_states_clear_node().
> But we do this after rebuilding the zonelists by calling
> build_all_zonelists(), which will cause this memoryless node to
> still be in the fallback list of other nodes. This will incur
> some runtime overhead.
> 
> To drop memoryless node from fallback lists in this case, just
> call node_states_clear_node() before calling build_all_zonelists().

s/memoryless node
 /memoryless nodes

> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d4a364fdaf8f..f019f7d6272c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -2036,12 +2036,16 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  	/* reinitialise watermarks and update pcp limits */
>  	init_per_zone_wmark_min();
>  
> +	/*
> +	 * Make sure to mark the node as memory-less before rebuilding the zone
> +	 * list. Otherwise this node would still appear in the fallback lists.
> +	 */
> +	node_states_clear_node(node, &arg);

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

Re: [PATCH v3 1/2] mm: page_alloc: skip memoryless nodes entirely

[Qi Zheng]

On 2023/10/20 16:31, Ingo Molnar wrote:
> 
> * Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
>> In find_next_best_node(), We skipped the memoryless nodes
> 
> s/We
>   /we
> 
> s/the memoryless nodes
>   /memoryless nodes
> 
>> when building the zonelists of other normal nodes (N_NORMAL),
>> but did not skip the memoryless node itself when building
>> the zonelist. This will cause it to be traversed at runtime.
>>
>> For example, say we have node0 and node1, node0 is memoryless
>> node, then the fallback order of node0 and node1 as follows:
>>
>> [    0.153005] Fallback order for Node 0: 0 1
>> [    0.153564] Fallback order for Node 1: 1
>>
>> After this patch, we skip memoryless node0 entirely, then
>> the fallback order of node0 and node1 as follows:
> 
> s/fallback
>   /fall back
> 
>>
>> [    0.155236] Fallback order for Node 0: 1
>> [    0.155806] Fallback order for Node 1: 1
>>
>> So it becomes completely invisible, which will reduce runtime
>> overhead.
>>
>> And in this way, we will not try to allocate pages from memoryless
>> node0, then the panic mentioned in [1] will also be fixed. Even though
>> this problem has been solved by dropping the NODE_MIN_SIZE constrain
>> in x86 [2], it would be better to fix it in core MM as well.
> 
> s/in core MM
>   /in the core MM
> 
>> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
>> [2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
> 
>> +	/*
>> +	 * Use the local node if we haven't already. But for memoryless local
>> +	 * node, we should skip it and fallback to other nodes.
> 
> s/fallback
>   /fall back
> 
> s/already. But
>   /already, but

Will fix the typos above.

> 
> Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks.

> 
> Thanks,
> 
> 	Ingo

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Qi Zheng]

Hi Ingo,

On 2023/10/20 16:32, Ingo Molnar wrote:
> 
> * Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
>> In offline_pages(), if a node becomes memoryless, we
>> will clear its N_MEMORY state by calling node_states_clear_node().
>> But we do this after rebuilding the zonelists by calling
>> build_all_zonelists(), which will cause this memoryless node to
>> still be in the fallback list of other nodes. This will incur
>> some runtime overhead.
>>
>> To drop memoryless node from fallback lists in this case, just
>> call node_states_clear_node() before calling build_all_zonelists().
> 
> s/memoryless node
>   /memoryless nodes

Will do.

> 
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> ---
>>   mm/memory_hotplug.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index d4a364fdaf8f..f019f7d6272c 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -2036,12 +2036,16 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>>   	/* reinitialise watermarks and update pcp limits */
>>   	init_per_zone_wmark_min();
>>   
>> +	/*
>> +	 * Make sure to mark the node as memory-less before rebuilding the zone
>> +	 * list. Otherwise this node would still appear in the fallback lists.
>> +	 */
>> +	node_states_clear_node(node, &arg);
> 
> Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks.

> 
> Thanks,
> 
> 	Ingo

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Huang, Ying]

Qi Zheng <zhengqi.arch@bytedance.com> writes:

> Hi Ying,
>
> On 2023/10/20 15:05, Huang, Ying wrote:
>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>> 
>>> In offline_pages(), if a node becomes memoryless, we
>>> will clear its N_MEMORY state by calling node_states_clear_node().
>>> But we do this after rebuilding the zonelists by calling
>>> build_all_zonelists(), which will cause this memoryless node to
>>> still be in the fallback list of other nodes.
>> For fallback list, do you mean pgdat->node_zonelists[]?  If so, in
>> build_all_zonelists
>>    __build_all_zonelists
>>      build_zonelists
>>        build_zonelists_in_node_order
>>          build_zonerefs_node
>> populated_zone() will be checked before adding zone into zonelist.
>> So, IIUC, we will not try to allocate from the memory less node.
>
> Normally yes, but if it is the weird topology mentioned in [1], it's
> possible to allocate memory from it, it is a memoryless node, but it
> also has memory.
>
> In addition to the above case, I think it's reasonable to remove
> memory less node from node_order[] in advance. In this way it will
> not to be traversed in build_zonelists_in_node_order().
>
> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/

Got it!  Thank you for information.  I think that it may be good to
include this in the patch description to avoid potential confusing in
the future.

--
Best Regards,
Huang, Ying

> Thanks,
> Qi
>
>
>> --
>> Best Regards,
>> Huang, Ying
>> 
>>> This will incur
>>> some runtime overhead.
>>>
>>> To drop memoryless node from fallback lists in this case, just
>>> call node_states_clear_node() before calling build_all_zonelists().
>>>
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> Acked-by: David Hildenbrand <david@redhat.com>
>> [snip]
>> --
>> Best Regards,
>> Huang, Ying

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Qi Zheng]

Hi Ying,

On 2023/10/23 09:18, Huang, Ying wrote:
> Qi Zheng <zhengqi.arch@bytedance.com> writes:
> 
>> Hi Ying,
>>
>> On 2023/10/20 15:05, Huang, Ying wrote:
>>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>>>
>>>> In offline_pages(), if a node becomes memoryless, we
>>>> will clear its N_MEMORY state by calling node_states_clear_node().
>>>> But we do this after rebuilding the zonelists by calling
>>>> build_all_zonelists(), which will cause this memoryless node to
>>>> still be in the fallback list of other nodes.
>>> For fallback list, do you mean pgdat->node_zonelists[]?  If so, in
>>> build_all_zonelists
>>>     __build_all_zonelists
>>>       build_zonelists
>>>         build_zonelists_in_node_order
>>>           build_zonerefs_node
>>> populated_zone() will be checked before adding zone into zonelist.
>>> So, IIUC, we will not try to allocate from the memory less node.
>>
>> Normally yes, but if it is the weird topology mentioned in [1], it's
>> possible to allocate memory from it, it is a memoryless node, but it
>> also has memory.
>>
>> In addition to the above case, I think it's reasonable to remove
>> memory less node from node_order[] in advance. In this way it will
>> not to be traversed in build_zonelists_in_node_order().
>>
>> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
> 
> Got it!  Thank you for information.  I think that it may be good to
> include this in the patch description to avoid potential confusing in
> the future.

OK, maybe the commit message can be changed to the following:

```
In offline_pages(), if a node becomes memoryless, we
will clear its N_MEMORY state by calling node_states_clear_node().
But we do this after rebuilding the zonelists by calling
build_all_zonelists(), which will cause this memoryless node to
still be in the fallback nodes (node_order[]) of other nodes.

To drop memoryless nodes from fallback nodes in this case, just
call node_states_clear_node() before calling build_all_zonelists().

In this way, we will not try to allocate pages from memoryless
node0, then the panic mentioned in [1] will also be fixed. Even though
this problem has been solved by dropping the NODE_MIN_SIZE constrain
in x86 [2], it would be better to fix it in the core MM as well.

[1]. 
https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
[2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/

```

Thanks,
Qi

> 
> --
> Best Regards,
> Huang, Ying
> 
>> Thanks,
>> Qi
>>
>>
>>> --
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> This will incur
>>>> some runtime overhead.
>>>>
>>>> To drop memoryless node from fallback lists in this case, just
>>>> call node_states_clear_node() before calling build_all_zonelists().
>>>>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>> [snip]
>>> --
>>> Best Regards,
>>> Huang, Ying

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Huang, Ying]

Qi Zheng <zhengqi.arch@bytedance.com> writes:

> Hi Ying,
>
> On 2023/10/23 09:18, Huang, Ying wrote:
>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>> 
>>> Hi Ying,
>>>
>>> On 2023/10/20 15:05, Huang, Ying wrote:
>>>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>>>>
>>>>> In offline_pages(), if a node becomes memoryless, we
>>>>> will clear its N_MEMORY state by calling node_states_clear_node().
>>>>> But we do this after rebuilding the zonelists by calling
>>>>> build_all_zonelists(), which will cause this memoryless node to
>>>>> still be in the fallback list of other nodes.
>>>> For fallback list, do you mean pgdat->node_zonelists[]?  If so, in
>>>> build_all_zonelists
>>>>     __build_all_zonelists
>>>>       build_zonelists
>>>>         build_zonelists_in_node_order
>>>>           build_zonerefs_node
>>>> populated_zone() will be checked before adding zone into zonelist.
>>>> So, IIUC, we will not try to allocate from the memory less node.
>>>
>>> Normally yes, but if it is the weird topology mentioned in [1], it's
>>> possible to allocate memory from it, it is a memoryless node, but it
>>> also has memory.
>>>
>>> In addition to the above case, I think it's reasonable to remove
>>> memory less node from node_order[] in advance. In this way it will
>>> not to be traversed in build_zonelists_in_node_order().
>>>
>>> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
>> Got it!  Thank you for information.  I think that it may be good to
>> include this in the patch description to avoid potential confusing in
>> the future.
>
> OK, maybe the commit message can be changed to the following:
>
> ```
> In offline_pages(), if a node becomes memoryless, we
> will clear its N_MEMORY state by calling node_states_clear_node().
> But we do this after rebuilding the zonelists by calling
> build_all_zonelists(), which will cause this memoryless node to
> still be in the fallback nodes (node_order[]) of other nodes.
>
> To drop memoryless nodes from fallback nodes in this case, just
> call node_states_clear_node() before calling build_all_zonelists().
>
> In this way, we will not try to allocate pages from memoryless
> node0, then the panic mentioned in [1] will also be fixed. Even though
> this problem has been solved by dropping the NODE_MIN_SIZE constrain
> in x86 [2], it would be better to fix it in the core MM as well.
>
> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
> [2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/
>
> ```

This is helpful.  Thanks!

--
Best Regards,
Huang, Ying

> Thanks,
> Qi
>
>> --
>> Best Regards,
>> Huang, Ying
>> 
>>> Thanks,
>>> Qi
>>>
>>>
>>>> --
>>>> Best Regards,
>>>> Huang, Ying
>>>>
>>>>> This will incur
>>>>> some runtime overhead.
>>>>>
>>>>> To drop memoryless node from fallback lists in this case, just
>>>>> call node_states_clear_node() before calling build_all_zonelists().
>>>>>
>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>>> [snip]
>>>> --
>>>> Best Regards,
>>>> Huang, Ying

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Qi Zheng]

On 2023/10/23 11:10, Huang, Ying wrote:
> Qi Zheng <zhengqi.arch@bytedance.com> writes:
> 
>> Hi Ying,
>>
>> On 2023/10/23 09:18, Huang, Ying wrote:
>>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>>>
>>>> Hi Ying,
>>>>
>>>> On 2023/10/20 15:05, Huang, Ying wrote:
>>>>> Qi Zheng <zhengqi.arch@bytedance.com> writes:
>>>>>
>>>>>> In offline_pages(), if a node becomes memoryless, we
>>>>>> will clear its N_MEMORY state by calling node_states_clear_node().
>>>>>> But we do this after rebuilding the zonelists by calling
>>>>>> build_all_zonelists(), which will cause this memoryless node to
>>>>>> still be in the fallback list of other nodes.
>>>>> For fallback list, do you mean pgdat->node_zonelists[]?  If so, in
>>>>> build_all_zonelists
>>>>>      __build_all_zonelists
>>>>>        build_zonelists
>>>>>          build_zonelists_in_node_order
>>>>>            build_zonerefs_node
>>>>> populated_zone() will be checked before adding zone into zonelist.
>>>>> So, IIUC, we will not try to allocate from the memory less node.
>>>>
>>>> Normally yes, but if it is the weird topology mentioned in [1], it's
>>>> possible to allocate memory from it, it is a memoryless node, but it
>>>> also has memory.
>>>>
>>>> In addition to the above case, I think it's reasonable to remove
>>>> memory less node from node_order[] in advance. In this way it will
>>>> not to be traversed in build_zonelists_in_node_order().
>>>>
>>>> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
>>> Got it!  Thank you for information.  I think that it may be good to
>>> include this in the patch description to avoid potential confusing in
>>> the future.
>>
>> OK, maybe the commit message can be changed to the following:
>>
>> ```
>> In offline_pages(), if a node becomes memoryless, we
>> will clear its N_MEMORY state by calling node_states_clear_node().
>> But we do this after rebuilding the zonelists by calling
>> build_all_zonelists(), which will cause this memoryless node to
>> still be in the fallback nodes (node_order[]) of other nodes.
>>
>> To drop memoryless nodes from fallback nodes in this case, just
>> call node_states_clear_node() before calling build_all_zonelists().
>>
>> In this way, we will not try to allocate pages from memoryless
>> node0, then the panic mentioned in [1] will also be fixed. Even though
>> this problem has been solved by dropping the NODE_MIN_SIZE constrain
>> in x86 [2], it would be better to fix it in the core MM as well.
>>
>> [1]. https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
>> [2]. https://lore.kernel.org/all/20231017062215.171670-1-rppt@kernel.org/
>>
>> ```

Hi Andrew, can you help modify the commit message to this? :)

Thanks,
Qi

> 
> This is helpful.  Thanks!
> 
> --
> Best Regards,
> Huang, Ying
> 
>> Thanks,
>> Qi
>>
>>> --
>>> Best Regards,
>>> Huang, Ying
>>>
>>>> Thanks,
>>>> Qi
>>>>
>>>>
>>>>> --
>>>>> Best Regards,
>>>>> Huang, Ying
>>>>>
>>>>>> This will incur
>>>>>> some runtime overhead.
>>>>>>
>>>>>> To drop memoryless node from fallback lists in this case, just
>>>>>> call node_states_clear_node() before calling build_all_zonelists().
>>>>>>
>>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>>>> [snip]
>>>>> --
>>>>> Best Regards,
>>>>> Huang, Ying

Re: [PATCH v3 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[Andrew Morton]

On Mon, 23 Oct 2023 11:17:03 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> Hi Andrew, can you help modify the commit message to this? :)

Done, thanks.