[Patch](memory hotplug)Allocate usemap on the section with pgdat (take 3)

[Yasunori Goto]

Here is take 3 for usemap allocation on pgdat section.

If there is any trouble, please let me know.

If no trouble, please apply.

Thanks.

---

Usemaps are allocated on the section which has pgdat by this.

Because usemap size is very small, many other sections usemaps
are allocated on only one page. If a section has usemap, it
can't be removed until removing other sections.
This dependency is not desirable for memory removing.

Pgdat has similar feature. When a section has pgdat area, it 
must be the last section for removing on the node.
So, if section A has pgdat and section B has usemap for section A,
Both sections can't be removed due to dependency each other.

To solve this issue, this patch collects usemap on same
section with pgdat as much as possible.
If other sections doesn't have any dependency, this section will
be able to be removed finally.

Change log of take 3.
 - Change dependency message and comment.
  (Thanks! > Andy Whitcroft-san)

Change log of take 2.
 - This feature becomes effective only when CONFIG_MEMORY_HOTREMOVE is on.
   If hotremove is off, this feature is not necessary.
 - Allow allocation on other section if alloc_bootmem_section() fails.
   This removes previous regression.
 - Show message if allocation on same section fails.

Signed-off-by: Yasunori Goto <y-goto@xxxxxxxxxxxxxx>

---

 mm/sparse.c |   78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 77 insertions(+), 1 deletion(-)

Index: current/mm/sparse.c
===================================================================
--- current.orig/mm/sparse.c	2008-06-17 15:34:29.000000000 +0900
+++ current/mm/sparse.c	2008-06-17 18:35:02.000000000 +0900
@@ -269,16 +269,92 @@
 }
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static unsigned long * __init
+sparse_early_usemap_alloc_section(unsigned long pnum)
+{
+	unsigned long section_nr;
+	struct mem_section *ms = __nr_to_section(pnum);
+	int nid = sparse_early_nid(ms);
+ 	struct pglist_data *pgdat = NODE_DATA(nid);
+
+	/*
+	 * Usemap's page can't be freed until freeing other sections
+	 * which use it. And, pgdat has same feature.
+	 * If section A has pgdat and section B has usemap for other
+	 * sections (includes section A), both sections can't be removed,
+	 * because there is the dependency each other.
+	 * To solve above issue, this collects all usemap on the same section
+	 * which has pgdat as much as possible.
+	 */
+	section_nr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
+	return alloc_bootmem_section(usemap_size(), section_nr);
+}
+
+static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+{
+	unsigned long usemap_snr, pgdat_snr;
+	static unsigned long old_usemap_snr = NR_MEM_SECTIONS;
+	static unsigned long old_pgdat_snr = NR_MEM_SECTIONS;
+	struct pglist_data *pgdat = NODE_DATA(nid);
+	int usemap_nid;
+
+	usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
+	pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
+	if (usemap_snr == pgdat_snr)
+		return;
+
+	if (old_usemap_snr == usemap_snr && old_pgdat_snr == pgdat_snr)
+		/* skip redundant message */
+		return;
+
+	old_usemap_snr = usemap_snr;
+	old_pgdat_snr = pgdat_snr;
+
+	usemap_nid = sparse_early_nid(__nr_to_section(usemap_snr));
+	if (usemap_nid != nid) {
+		printk("node %d must be removed before remove section %ld\n",
+		       nid, usemap_snr);
+		return;
+	}
+	/*
+	 * There is a circular dependency.
+	 * Some platforms allow un-removable section because they will just
+	 * gather other removable sections for dynamic partitioning.
+	 * Just notify un-removable section's number here.
+	 */
+	printk(KERN_INFO "Section %ld and %ld (node %d)",
+	       usemap_snr, pgdat_snr, nid);
+	printk(" have a circular dependency on usemap and pgdat allocations\n");
+}
+#else
+static unsigned long * __init
+sparse_early_usemap_alloc_section(unsigned long pnum)
+{
+	return NULL;
+}
+
+static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+{
+}
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
 static unsigned long *__init sparse_early_usemap_alloc(unsigned long pnum)
 {
 	unsigned long *usemap;
 	struct mem_section *ms = __nr_to_section(pnum);
 	int nid = sparse_early_nid(ms);
 
-	usemap = alloc_bootmem_node(NODE_DATA(nid), usemap_size());
+	usemap = sparse_early_usemap_alloc_section(pnum);
 	if (usemap)
 		return usemap;
 
+	usemap = alloc_bootmem_node(NODE_DATA(nid), usemap_size());
+	if (usemap) {
+		check_usemap_section_nr(nid, usemap);
+		return usemap;
+	}
+
 	/* Stupid: suppress gcc warning for SPARSEMEM && !NUMA */
 	nid = 0;
 

-- 
Yasunori Goto 


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