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Commit 5c755e9f authored by Badari Pulavarty's avatar Badari Pulavarty Committed by Linus Torvalds
Browse files

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 <pbadari@us.ibm.com>
Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2f7f24ec

Documentation/ABI/testing/sysfs-devices-memory

0 → 100644
+24 −0
Original line number Diff line number Diff line 
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/

drivers/base/memory.c

+19 −0
Original line number Diff line number Diff line
@@ -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;

include/linux/memory_hotplug.h

+12 −0
Original line number Diff line number Diff line
@@ -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 *));



#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);

mm/memory_hotplug.c

+60 −0
Original line number Diff line number Diff line
@@ -522,6 +522,66 @@ error: 
EXPORT_SYMBOL_GPL(add_memory);



#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.

 */