memory-hotplug: add sysfs removable attribute for hotplug memory remove
Memory may be hot-removed on a per-memory-block basis, particularly on
POWER where the SPARSEMEM section size often matches the memory-block
size. A user-level agent must be able to identify which sections of
memory are likely to be removable before attempting the potentially
expensive operation. This patch adds a file called "removable" to the
memory directory in sysfs to help such an agent. In this patch, a memory
block is considered removable if;
o It contains only MOVABLE pageblocks
o It contains only pageblocks with free pages regardless of pageblock type
On the other hand, a memory block starting with a PageReserved() page will
never be considered removable. Without this patch, the user-agent is
forced to choose a memory block to remove randomly.
Sample output of the sysfs files:
./memory/memory0/removable: 0
./memory/memory1/removable: 0
./memory/memory2/removable: 0
./memory/memory3/removable: 0
./memory/memory4/removable: 0
./memory/memory5/removable: 0
./memory/memory6/removable: 0
./memory/memory7/removable: 1
./memory/memory8/removable: 0
./memory/memory9/removable: 0
./memory/memory10/removable: 0
./memory/memory11/removable: 0
./memory/memory12/removable: 0
./memory/memory13/removable: 0
./memory/memory14/removable: 0
./memory/memory15/removable: 0
./memory/memory16/removable: 0
./memory/memory17/removable: 1
./memory/memory18/removable: 1
./memory/memory19/removable: 1
./memory/memory20/removable: 1
./memory/memory21/removable: 1
./memory/memory22/removable: 1
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
new file mode 100644
index 0000000..7a16fe1
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -0,0 +1,24 @@
+What: /sys/devices/system/memory
+Date: June 2008
+Contact: Badari Pulavarty <pbadari@us.ibm.com>
+Description:
+ The /sys/devices/system/memory contains a snapshot of the
+ internal state of the kernel memory blocks. Files could be
+ added or removed dynamically to represent hot-add/remove
+ operations.
+
+Users: hotplug memory add/remove tools
+ https://w3.opensource.ibm.com/projects/powerpc-utils/
+
+What: /sys/devices/system/memory/memoryX/removable
+Date: June 2008
+Contact: Badari Pulavarty <pbadari@us.ibm.com>
+Description:
+ The file /sys/devices/system/memory/memoryX/removable
+ indicates whether this memory block is removable or not.
+ This is useful for a user-level agent to determine
+ identify removable sections of the memory before attempting
+ potentially expensive hot-remove memory operation
+
+Users: hotplug memory remove tools
+ https://w3.opensource.ibm.com/projects/powerpc-utils/
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 4d4e0e7..855ed1a9 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -101,6 +101,21 @@
}
/*
+ * Show whether the section of memory is likely to be hot-removable
+ */
+static ssize_t show_mem_removable(struct sys_device *dev, char *buf)
+{
+ unsigned long start_pfn;
+ int ret;
+ struct memory_block *mem =
+ container_of(dev, struct memory_block, sysdev);
+
+ start_pfn = section_nr_to_pfn(mem->phys_index);
+ ret = is_mem_section_removable(start_pfn, PAGES_PER_SECTION);
+ return sprintf(buf, "%d\n", ret);
+}
+
+/*
* online, offline, going offline, etc.
*/
static ssize_t show_mem_state(struct sys_device *dev,
@@ -262,6 +277,7 @@
static SYSDEV_ATTR(phys_index, 0444, show_mem_phys_index, NULL);
static SYSDEV_ATTR(state, 0644, show_mem_state, store_mem_state);
static SYSDEV_ATTR(phys_device, 0444, show_phys_device, NULL);
+static SYSDEV_ATTR(removable, 0444, show_mem_removable, NULL);
#define mem_create_simple_file(mem, attr_name) \
sysdev_create_file(&mem->sysdev, &attr_##attr_name)
@@ -350,6 +366,8 @@
ret = mem_create_simple_file(mem, state);
if (!ret)
ret = mem_create_simple_file(mem, phys_device);
+ if (!ret)
+ ret = mem_create_simple_file(mem, removable);
return ret;
}
@@ -394,6 +412,7 @@
mem_remove_simple_file(mem, phys_index);
mem_remove_simple_file(mem, state);
mem_remove_simple_file(mem, phys_device);
+ mem_remove_simple_file(mem, removable);
unregister_memory(mem, section);
return 0;
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 3628e50..763ba81 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -199,6 +199,18 @@
unsigned long nr_pages, void *arg,
int (*func)(unsigned long, unsigned long, void *));
+#ifdef CONFIG_MEMORY_HOTREMOVE
+
+extern int is_mem_section_removable(unsigned long pfn, unsigned long nr_pages);
+
+#else
+static inline int is_mem_section_removable(unsigned long pfn,
+ unsigned long nr_pages)
+{
+ return 0;
+}
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
extern int add_memory(int nid, u64 start, u64 size);
extern int arch_add_memory(int nid, u64 start, u64 size);
extern int remove_memory(u64 start, u64 size);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 93aba78..89fee2d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -523,6 +523,66 @@
#ifdef CONFIG_MEMORY_HOTREMOVE
/*
+ * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy
+ * set and the size of the free page is given by page_order(). Using this,
+ * the function determines if the pageblock contains only free pages.
+ * Due to buddy contraints, a free page at least the size of a pageblock will
+ * be located at the start of the pageblock
+ */
+static inline int pageblock_free(struct page *page)
+{
+ return PageBuddy(page) && page_order(page) >= pageblock_order;
+}
+
+/* Return the start of the next active pageblock after a given page */
+static struct page *next_active_pageblock(struct page *page)
+{
+ int pageblocks_stride;
+
+ /* Ensure the starting page is pageblock-aligned */
+ BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));
+
+ /* Move forward by at least 1 * pageblock_nr_pages */
+ pageblocks_stride = 1;
+
+ /* If the entire pageblock is free, move to the end of free page */
+ if (pageblock_free(page))
+ pageblocks_stride += page_order(page) - pageblock_order;
+
+ return page + (pageblocks_stride * pageblock_nr_pages);
+}
+
+/* Checks if this range of memory is likely to be hot-removable. */
+int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
+{
+ int type;
+ struct page *page = pfn_to_page(start_pfn);
+ struct page *end_page = page + nr_pages;
+
+ /* Check the starting page of each pageblock within the range */
+ for (; page < end_page; page = next_active_pageblock(page)) {
+ type = get_pageblock_migratetype(page);
+
+ /*
+ * A pageblock containing MOVABLE or free pages is considered
+ * removable
+ */
+ if (type != MIGRATE_MOVABLE && !pageblock_free(page))
+ return 0;
+
+ /*
+ * A pageblock starting with a PageReserved page is not
+ * considered removable.
+ */
+ if (PageReserved(page))
+ return 0;
+ }
+
+ /* All pageblocks in the memory block are likely to be hot-removable */
+ return 1;
+}
+
+/*
* Confirm all pages in a range [start, end) is belongs to the same zone.
*/
static int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
