Re: [RFC PATCH 2/2] mm, memory_hotplug: drop CONFIG_MOVABLE_NODE

[Michal Hocko]

On Wed 24-05-17 14:53:57, Vlastimil Babka wrote:
> On 05/24/2017 02:24 PM, Michal Hocko wrote:
[...]
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index facc20a3f962..ec7d6ae01c96 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2246,8 +2246,11 @@
> >  			that the amount of memory usable for all allocations
> >  			is not too small.
> >  
> > -	movable_node	[KNL] Boot-time switch to enable the effects
> > -			of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
> > +	movable_node	[KNL] Boot-time switch to make hotplugable to be
> 
> 			hotplugable what, memory? nodes?


diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ec7d6ae01c96..64aed7386fe4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2246,11 +2246,11 @@
 			that the amount of memory usable for all allocations
 			is not too small.
 
-	movable_node	[KNL] Boot-time switch to make hotplugable to be
-			movable. This means that the memory of such nodes
-			will be usable only for movable allocations which
-			rules out almost all kernel allocations. Use with
-			caution!
+	movable_node	[KNL] Boot-time switch to make hotplugable memory
+			NUMA nodes to be movable. This means that the memory
+			of such nodes will be usable only for movable
+			allocations which rules out almost all kernel
+			allocations. Use with caution!
 
 	MTD_Partition=	[MTD]
 			Format: <name>,<region-number>,<size>,<offset>

Better?

[...]
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -149,32 +149,6 @@ config NO_BOOTMEM
> >  config MEMORY_ISOLATION
> >  	bool
> >  
> > -config MOVABLE_NODE
> > -	bool "Enable to assign a node which has only movable memory"
> > -	depends on HAVE_MEMBLOCK
> > -	depends on NO_BOOTMEM
> > -	depends on X86_64 || OF_EARLY_FLATTREE || MEMORY_HOTPLUG
> > -	depends on NUMA
> 
> That's a lot of depends. What happens if some of them are not met and
> the movable_node bootparam is used?

Good question. I haven't explored that, to be honest. Now that I am looking closer
I am not even sure why all those dependencies are thre. MEMORY_HOTPLUG
is clear and OF_EARLY_FLATTREE is explained by 41a9ada3e6b4 ("of/fdt:
mark hotpluggable memory"). NUMA is less clear to me because
MEMORY_HOTPLUG doesn't really depend on NUMA systems. Dependency on
NO_BOOTMEM is also not clear to me because zones layout
doesn't really depend on the specific boot time allocator.

So we are left with HAVE_MEMBLOCK which seems to be there because
movable_node_enabled is defined there while the parameter handling is in
the hotplug proper. But there is no real reason to have it like that.
This compiles but I will have to put throw my full compile battery on it
to be sure. I will make it a separate patch.

Thanks!
--- 
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 9622fb8c101b..071692894254 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -57,8 +57,6 @@ struct memblock {
 
 extern struct memblock memblock;
 extern int memblock_debug;
-/* If movable_node boot option specified */
-extern bool movable_node_enabled;
 
 #ifdef CONFIG_ARCH_DISCARD_MEMBLOCK
 #define __init_memblock __meminit
@@ -171,11 +169,6 @@ static inline bool memblock_is_hotpluggable(struct memblock_region *m)
 	return m->flags & MEMBLOCK_HOTPLUG;
 }
 
-static inline bool __init_memblock movable_node_is_enabled(void)
-{
-	return movable_node_enabled;
-}
-
 static inline bool memblock_is_mirror(struct memblock_region *m)
 {
 	return m->flags & MEMBLOCK_MIRROR;
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 9e0249d0f5e4..9c1ac94f857b 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -115,6 +115,12 @@ extern void __online_page_free(struct page *page);
 extern int try_online_node(int nid);
 
 extern bool memhp_auto_online;
+/* If movable_node boot option specified */
+extern bool movable_node_enabled;
+static inline bool movable_node_is_enabled(void)
+{
+	return movable_node_enabled;
+}
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
 extern bool is_pageblock_removable_nolock(struct page *page);
@@ -266,6 +272,10 @@ static inline void put_online_mems(void) {}
 static inline void mem_hotplug_begin(void) {}
 static inline void mem_hotplug_done(void) {}
 
+static inline bool __init_memblock movable_node_is_enabled(void)
+{
+	return false;
+}
 #endif /* ! CONFIG_MEMORY_HOTPLUG */
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
diff --git a/mm/memblock.c b/mm/memblock.c
index 4895f5a6cf7e..8c52fb11510c 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -54,7 +54,6 @@ struct memblock memblock __initdata_memblock = {
 };
 
 int memblock_debug __initdata_memblock;
-bool movable_node_enabled __initdata_memblock = false;
 static bool system_has_some_mirror __initdata_memblock = false;
 static int memblock_can_resize __initdata_memblock;
 static int memblock_memory_in_slab __initdata_memblock = 0;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2a14f8c18a22..b0d2bf3256d0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -79,6 +79,8 @@ static struct {
 #define memhp_lock_acquire()      lock_map_acquire(&mem_hotplug.dep_map)
 #define memhp_lock_release()      lock_map_release(&mem_hotplug.dep_map)
 
+bool movable_node_enabled = false;
+
 #ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
 bool memhp_auto_online;
 #else

-- 
Michal Hocko
SUSE Labs