On Tue, 2013-08-27 at 13:44 +1000, Benjamin Herrenschmidt wrote:

So I still feel very uncomfortable with that stuff ....

For example, x86 calls register_page_bootmem_info_node() at boot time,
which does that strange "get_page_bootmem" on the NODE_DATA itself at
boot time, we don't. Should we ?

Bah, call me an idiot ... I was looking at the code without your patch
and not realizing that this is exactly what your patch does :-)

 .../...

There's a whole pile of totally undocumented / uncommented generic code
with horrible function names in there whose sematic is very very
unclear.

Now, if we call that thing, are we expected to have
register_paqe_bootmem_memmap() to actually do something right? I assume
that means actually calling get_page_bootmem() on the various struct
page that comprise the vmemmap.

Well, we can probably implement that since we maintain a list of all the
vmemap pages... However, we don't implement vmemmap_free(). Should we ?

This still stands, should we actually "register" the pages of the
vmemmap or not ?

What happens if we remove a chunk of memory and then plug it back in ?
Will it try to re-create a new vmemmap chunk for that area (where we
haven't removed the previous one) ? That might cause problems if we end
up putting duplicate entries in the hash table ... should we implement
vmemmap_free and actual unmap the segments ?

Cheers,
Ben.

quoted

---
 arch/powerpc/mm/init_64.c |    4 ++++
 arch/powerpc/mm/mem.c     |    9 +++++++++
 mm/Kconfig                |    2 +-
 3 files changed, 14 insertions(+), 1 deletion(-)

Index: linux/arch/powerpc/mm/init_64.c
===================================================================

--- linux.orig/arch/powerpc/mm/init_64.c
+++ linux/arch/powerpc/mm/init_64.c

@@ -300,5 +300,9 @@ void vmemmap_free(unsigned long start, u
 {
 }

+void register_page_bootmem_memmap(unsigned long section_nr,
+				  struct page *start_page, unsigned long size)
+{
+}
 #endif /* CONFIG_SPARSEMEM_VMEMMAP */

Index: linux/arch/powerpc/mm/mem.c
===================================================================

--- linux.orig/arch/powerpc/mm/mem.c
+++ linux/arch/powerpc/mm/mem.c

@@ -297,12 +297,21 @@ void __init paging_init(void)
 }
 #endif /* ! CONFIG_NEED_MULTIPLE_NODES */

+static void __init register_page_bootmem_info(void)
+{
+	int i;
+
+	for_each_online_node(i)
+		register_page_bootmem_info_node(NODE_DATA(i));
+}
+
 void __init mem_init(void)
 {
 #ifdef CONFIG_SWIOTLB
 	swiotlb_init(0);
 #endif

+	register_page_bootmem_info();
 	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
 	set_max_mapnr(max_pfn);
 	free_all_bootmem();

Index: linux/mm/Kconfig
===================================================================

--- linux.orig/mm/Kconfig
+++ linux/mm/Kconfig

@@ -183,7 +183,7 @@ config MEMORY_HOTPLUG_SPARSE
 config MEMORY_HOTREMOVE
 	bool "Allow for memory hot remove"
 	select MEMORY_ISOLATION
-	select HAVE_BOOTMEM_INFO_NODE if X86_64
+	select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 	depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 	depends on MIGRATION

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