Commit 5c755e9f authored by Badari Pulavarty's avatar Badari Pulavarty Committed by Linus Torvalds
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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: default avatarBadari Pulavarty <>
Signed-off-by: default avatarMel Gorman <>
Acked-by: default avatarKAMEZAWA Hiroyuki <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 2f7f24ec
What: /sys/devices/system/memory
Date: June 2008
Contact: Badari Pulavarty <>
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
Users: hotplug memory add/remove tools
What: /sys/devices/system/memory/memoryX/removable
Date: June 2008
Contact: Badari Pulavarty <>
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
......@@ -100,6 +100,21 @@ static ssize_t show_mem_phys_index(struct sys_device *dev,
return sprintf(buf, "%08lx\n", mem->phys_index);
* 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.
......@@ -262,6 +277,7 @@ static ssize_t show_phys_device(struct sys_device *dev,
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 @@ static int add_memory_block(unsigned long node_id, struct mem_section *section,
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 @@ int remove_memory_block(unsigned long node_id, struct mem_section *section,
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;
......@@ -199,6 +199,18 @@ extern int walk_memory_resource(unsigned long start_pfn,
unsigned long nr_pages, void *arg,
int (*func)(unsigned long, unsigned long, void *));
extern int is_mem_section_removable(unsigned long pfn, unsigned long nr_pages);
static inline int is_mem_section_removable(unsigned long pfn,
unsigned long nr_pages)
return 0;
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);
......@@ -522,6 +522,66 @@ int add_memory(int nid, u64 start, u64 size)
* 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.
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