Re: [PATCH v3 10/11] mm/memory_hotplug: Make unregister_memory_block_under_nodes() never fail

[Wei Yang]

On Mon, May 27, 2019 at 01:11:51PM +0200, David Hildenbrand wrote:
>We really don't want anything during memory hotunplug to fail.
>We always pass a valid memory block device, that check can go. Avoid
>allocating memory and eventually failing. As we are always called under
>lock, we can use a static piece of memory. This avoids having to put
>the structure onto the stack, having to guess about the stack size
>of callers.
>
>Patch inspired by a patch from Oscar Salvador.
>
>In the future, there might be no need to iterate over nodes at all.
>mem->nid should tell us exactly what to remove. Memory block devices
>with mixed nodes (added during boot) should properly fenced off and never
>removed.
>
>Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
>Cc: Alex Deucher <alexander.deucher@xxxxxxx>
>Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>Cc: Mark Brown <broonie@xxxxxxxxxx>
>Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>Cc: David Hildenbrand <david@xxxxxxxxxx>
>Cc: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>

>---
> drivers/base/node.c  | 18 +++++-------------
> include/linux/node.h |  5 ++---
> 2 files changed, 7 insertions(+), 16 deletions(-)
>
>diff --git a/drivers/base/node.c b/drivers/base/node.c
>index 04fdfa99b8bc..9be88fd05147 100644
>--- a/drivers/base/node.c
>+++ b/drivers/base/node.c
>@@ -803,20 +803,14 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
> 
> /*
>  * Unregister memory block device under all nodes that it spans.
>+ * Has to be called with mem_sysfs_mutex held (due to unlinked_nodes).
>  */
>-int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>+void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> {
>-	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
> 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
>+	static nodemask_t unlinked_nodes;
> 
>-	if (!mem_blk) {
>-		NODEMASK_FREE(unlinked_nodes);
>-		return -EFAULT;
>-	}
>-	if (!unlinked_nodes)
>-		return -ENOMEM;
>-	nodes_clear(*unlinked_nodes);
>-
>+	nodes_clear(unlinked_nodes);
> 	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
> 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
> 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
>@@ -827,15 +821,13 @@ int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> 			continue;
> 		if (!node_online(nid))
> 			continue;
>-		if (node_test_and_set(nid, *unlinked_nodes))
>+		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));
> 	}
>-	NODEMASK_FREE(unlinked_nodes);
>-	return 0;
> }
> 
> int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
>diff --git a/include/linux/node.h b/include/linux/node.h
>index 02a29e71b175..548c226966a2 100644
>--- a/include/linux/node.h
>+++ b/include/linux/node.h
>@@ -139,7 +139,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
> extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
> extern int register_mem_sect_under_node(struct memory_block *mem_blk,
> 						void *arg);
>-extern int unregister_memory_block_under_nodes(struct memory_block *mem_blk);
>+extern void unregister_memory_block_under_nodes(struct memory_block *mem_blk);
> 
> extern int register_memory_node_under_compute_node(unsigned int mem_nid,
> 						   unsigned int cpu_nid,
>@@ -175,9 +175,8 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk,
> {
> 	return 0;
> }
>-static inline int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>+static inline void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> {
>-	return 0;
> }
> 
> static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
>-- 
>2.20.1

-- 
Wei Yang
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