[3/3] mm/memory_hotplug: Cleanup unregister_mem_sect_under_nodes
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Message ID 20180810152931.23004-4-osalvador@techadventures.net
State New
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Series
  • Refactor/cleanup for remove_memory_section/unregister_mem_sect_under_nodes
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Commit Message

Oscar Salvador Aug. 10, 2018, 3:29 p.m. UTC
From: Oscar Salvador <osalvador@suse.de>

With the assumption that the relationship between
memory_block <-> node is 1:1, we can refactor this function a bit.

This assumption is being taken from register_mem_sect_under_node()
code.

register_mem_sect_under_node() takes the mem_blk's nid, and compares it
to the pfn's nid we are checking.
If they match, we go ahead and link both objects.
Once done, we just return.

So, the relationship between memory_block <-> node seems to stand.

Currently, unregister_mem_sect_under_nodes() defines a nodemask_t
which is being checked in the loop to see if we have already unliked certain node.
But since a memory_block can only belong to a node, we can drop the nodemask
and the check within the loop.

If we find a match between the mem_block->nid and the nid of the
pfn we are checking, we unlink the objects and return, as unlink the objects
once is enough.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 drivers/base/node.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

Comments

Andrew Morton Aug. 10, 2018, 10:37 p.m. UTC | #1
On Fri, 10 Aug 2018 17:29:31 +0200 osalvador@techadventures.net wrote:

> From: Oscar Salvador <osalvador@suse.de>
> 
> With the assumption that the relationship between
> memory_block <-> node is 1:1, we can refactor this function a bit.
> 
> This assumption is being taken from register_mem_sect_under_node()
> code.
> 
> register_mem_sect_under_node() takes the mem_blk's nid, and compares it
> to the pfn's nid we are checking.
> If they match, we go ahead and link both objects.
> Once done, we just return.
> 
> So, the relationship between memory_block <-> node seems to stand.
> 
> Currently, unregister_mem_sect_under_nodes() defines a nodemask_t
> which is being checked in the loop to see if we have already unliked certain node.

"unlinked a certain node"

> But since a memory_block can only belong to a node, we can drop the nodemask

"to a single node"?

> and the check within the loop.
> 
> If we find a match between the mem_block->nid and the nid of the
> pfn we are checking, we unlink the objects and return, as unlink the objects

"unlinking"

> once is enough.
> 
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -448,35 +448,27 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
>  	return 0;
>  }
>  
> -/* unregister memory section under all nodes that it spans */
> +/* unregister memory section from the node it belongs to */
>  int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
>  				    unsigned long phys_index)
>  {
> -	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
>  	unsigned long pfn, sect_start_pfn, sect_end_pfn;
> -
> -	if (!unlinked_nodes)
> -		return -ENOMEM;
> -	nodes_clear(*unlinked_nodes);
> +	int nid = mem_blk->nid;
>  
>  	sect_start_pfn = section_nr_to_pfn(phys_index);
>  	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
>  	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
> -		int nid;
> +		int page_nid = get_nid_for_pfn(pfn);
>  
> -		nid = get_nid_for_pfn(pfn);
> -		if (nid < 0)
> -			continue;
> -		if (!node_online(nid))
> -			continue;
> -		if (node_test_and_set(nid, *unlinked_nodes))
> -			continue;
> -		sysfs_remove_link(&node_devices[nid]->dev.kobj,
> -			 kobject_name(&mem_blk->dev.kobj));
> -		sysfs_remove_link(&mem_blk->dev.kobj,
> -			 kobject_name(&node_devices[nid]->dev.kobj));
> +		if (page_nid >= 0 && page_nid == nid) {
> +			sysfs_remove_link(&node_devices[nid]->dev.kobj,
> +				 kobject_name(&mem_blk->dev.kobj));
> +			sysfs_remove_link(&mem_blk->dev.kobj,
> +				 kobject_name(&node_devices[nid]->dev.kobj));
> +			break;
> +		}
>  	}
> -	NODEMASK_FREE(unlinked_nodes);
> +
>  	return 0;
>  }

I guess so.  But the node_online() check was silently removed?
Oscar Salvador Aug. 11, 2018, 8:08 a.m. UTC | #2
On Fri, Aug 10, 2018 at 03:37:27PM -0700, Andrew Morton wrote:
> I guess so.  But the node_online() check was silently removed?

A node can only get offline if all the memory and CPUs associated
with it are removed.

This is being checked in remove_memory()->try_offline_node().
There we check whether the node has still valid sections or not,
and if there are still CPUs associated to it.

In the case that either we still have valid sections or that we have
CPUs linked to this node, we do not offline it.

So we cannot really be removing a memory from a node that is offline,
that is why it is safe to drop the check.

It was my mistake not to explain that properly in the changelog though.
I will send a V2 fixing up all you pointed out and explaining
why it is safe to drop the check.

Thanks
Oscar Salvador Aug. 13, 2018, 8:55 a.m. UTC | #3
On Fri, Aug 10, 2018 at 05:29:31PM +0200, osalvador@techadventures.net wrote:
> From: Oscar Salvador <osalvador@suse.de>
> 
> With the assumption that the relationship between
> memory_block <-> node is 1:1, we can refactor this function a bit.
> 
> This assumption is being taken from register_mem_sect_under_node()
> code.

Doh, this assumption is wrong for boot case when a mem_blk can have
multiple sections.

Nevertheless, I think that unregister_mem_sect_under_nodes can be polished a bit.
I am working on that

Patch
diff mbox series

diff --git a/drivers/base/node.c b/drivers/base/node.c
index dd3bdab230b2..0657ed70bddd 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -448,35 +448,27 @@  int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
 	return 0;
 }
 
-/* unregister memory section under all nodes that it spans */
+/* unregister memory section from the node it belongs to */
 int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
 				    unsigned long phys_index)
 {
-	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
-
-	if (!unlinked_nodes)
-		return -ENOMEM;
-	nodes_clear(*unlinked_nodes);
+	int nid = mem_blk->nid;
 
 	sect_start_pfn = section_nr_to_pfn(phys_index);
 	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int nid;
+		int page_nid = get_nid_for_pfn(pfn);
 
-		nid = get_nid_for_pfn(pfn);
-		if (nid < 0)
-			continue;
-		if (!node_online(nid))
-			continue;
-		if (node_test_and_set(nid, *unlinked_nodes))
-			continue;
-		sysfs_remove_link(&node_devices[nid]->dev.kobj,
-			 kobject_name(&mem_blk->dev.kobj));
-		sysfs_remove_link(&mem_blk->dev.kobj,
-			 kobject_name(&node_devices[nid]->dev.kobj));
+		if (page_nid >= 0 && page_nid == nid) {
+			sysfs_remove_link(&node_devices[nid]->dev.kobj,
+				 kobject_name(&mem_blk->dev.kobj));
+			sysfs_remove_link(&mem_blk->dev.kobj,
+				 kobject_name(&node_devices[nid]->dev.kobj));
+			break;
+		}
 	}
-	NODEMASK_FREE(unlinked_nodes);
+
 	return 0;
 }