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>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 4d4e0e7b6e92..855ed1a9f97b 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -101,6 +101,21 @@ static ssize_t show_mem_phys_index(struct sys_device *dev,
 }
 
 /*
+ * 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 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;