Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

Laurent Dufour
2020-09-14T09:16:41Z

Le 14/09/2020 à 10:31, David Hildenbrand a écrit :
>>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>>> void *arg)
>>> {
>>> const int nid = *(int *)arg;
>>> int ret;
>>>
>>> /* Hotplugged memory has no holes and belongs to a single node. */
>>> mem_blk->nid = nid;
>>> ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>>> &mem_blk->dev.kobj,
>>> kobject_name(&mem_blk->dev.kobj));
>>> if (ret)
>>> returnr et;
>>> return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>>> &node_devices[nid]->dev.kobj,
>>> kobject_name(&node_devices[nid]->dev.kobj));
>>>
>>> }
>>>
>>> Cleaner, right? :) No unnecessary checks.
>>
>> I tend to agree here, I like more a simplistic version for hotplug.
>>
>
> ... and while we're at it, we should rename register_mem_sect_under_node
> to something like "register_memory_block_under_node" - "section" is a
> legacy leftover here.
>
> We could factor out both sysfs_create_link_nowarn() calls into something
> like "do_register_memory_block_under_node" or similar, to minimize code
> duplication.
>
>>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
>>
>> I am not sure if I would duplicate the code there.
>> We could just pass the pointer of the function we want to call to
>> link_mem_sections? either register_mem_sect_under_node_hotplug or
>> register_mem_sect_under_node_early?
>> Would not that be clean and clear enough?
>
> I don't particularly like passing around function pointers where it can
> be avoided (e.g., here exporting 3 functions now instead 1). Makes the
> interface harder to get IMHO. But I don't really care about that
> interface, easy to change later on.
>

This would lead to the following.

Do everyone agree?

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 508b80f6329b..444808a7c9b6 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -761,9 +761,32 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
return pfn_to_nid(pfn);
}

+static int do_register_memory_block_under_node(int nid,
+ struct memory_block *mem_blk)
+{
+ int ret;
+
+ /*
+ * If this memory block spans multiple nodes, we only indicate
+ * the last processed node.
+ */
+ mem_blk->nid = nid;
+
+ ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
+ &mem_blk->dev.kobj,
+ kobject_name(&mem_blk->dev.kobj));
+ if (ret)
+ return ret;
+
+ return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
+ &node_devices[nid]->dev.kobj,
+ kobject_name(&node_devices[nid]->dev.kobj));
+
+}
+
/* register memory section under specified node if it spans that node */
-static int register_mem_sect_under_node(struct memory_block *mem_blk,
- void *arg)
+static int register_mem_block_under_node_early(struct memory_block *mem_blk,
+ void *arg)
{
unsigned long memory_block_pfns = memory_block_size_bytes() / PAGE_SIZE;
unsigned long start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
@@ -785,38 +808,35 @@ static int register_mem_sect_under_node(struct
memory_block *mem_blk,
}

/*
- * We need to check if page belongs to nid only for the boot
- * case, during hotplug we know that all pages in the memory
- * block belong to the same node.
+ * We need to check if page belongs to nid only at the boot
+ * case because node's ranges can be interleaved.
*/
- if (system_state = SYSTEM_BOOTING) {
- page_nid = get_nid_for_pfn(pfn);
- if (page_nid < 0)
- continue;
- if (page_nid != nid)
- continue;
- }
-
- /*
- * If this memory block spans multiple nodes, we only indicate
- * the last processed node.
- */
- mem_blk->nid = nid;
+ page_nid = get_nid_for_pfn(pfn);
+ if (page_nid < 0)
+ continue;
+ if (page_nid != nid)
+ continue;

- ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
- &mem_blk->dev.kobj,
- kobject_name(&mem_blk->dev.kobj));
+ ret = do_register_memory_block_under_node(nid, mem_blk);
if (ret)
return ret;
-
- return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
- &node_devices[nid]->dev.kobj,
- kobject_name(&node_devices[nid]->dev.kobj));
}
/* mem section does not span the specified node */
return 0;
}

+/*
+ * During hotplug we know that all pages in the memory block belong to the same
+ * node.
+ */
+static int register_mem_block_under_node_hotplug(struct memory_block *mem_blk,
+ void *arg)
+{
+ int nid = *(int *)arg;
+
+ return do_register_memory_block_under_node(nid, mem_blk);
+}
+
/*
* Unregister a memory block device under the node it spans. Memory blocks
* with multiple nodes cannot be offlined and therefore also never be removed.
@@ -832,11 +852,19 @@ void unregister_memory_block_under_nodes(struct
memory_block *mem_blk)
kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
}

-int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
+int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
+ enum memplug_context context)
{
+ walk_memory_blocks_func_t func;
+
+ if (context = MEMPLUG_HOTPLUG)
+ func = register_mem_block_under_node_hotplug;
+ else
+ func = register_mem_block_under_node_early;
+
return walk_memory_blocks(PFN_PHYS(start_pfn),
PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
- register_mem_sect_under_node);
+ func);
}

#ifdef CONFIG_HUGETLBFS