Re: [RFC PATCH 4/12] memory-hotplug : remove /sys/firmware/memmap/Xsysfs

From: Yasuaki Ishimatsu
Date: Thu Jun 28 2012 - 04:08:23 EST

Hi Wen,

2012/06/28 15:32, Wen Congyang wrote:
At 06/27/2012 01:47 PM, Yasuaki Ishimatsu Wrote:
When (hot)adding memory into system, /sys/firmware/memmap/X/{end, start, type}
sysfs files are created. But there is no code to remove these files. The patch
implements the function to remove them.

Note : The code does not free firmware_map_entry since there is no way to free
memory which is allocated by bootmem.

CC: Len Brown <len.brown@xxxxxxxxx>
CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
CC: Paul Mackerras <paulus@xxxxxxxxx>
CC: Christoph Lameter <cl@xxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
CC: Wen Congyang <wency@xxxxxxxxxxxxxx>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>

---
drivers/firmware/memmap.c | 71 +++++++++++++++++++++++++++++++++++++++++++
include/linux/firmware-map.h | 6 +++
mm/memory_hotplug.c | 6 +++
3 files changed, 82 insertions(+), 1 deletion(-)

Index: linux-3.5-rc4/mm/memory_hotplug.c
===================================================================
--- linux-3.5-rc4.orig/mm/memory_hotplug.c 2012-06-26 13:37:30.546288901 +0900
+++ linux-3.5-rc4/mm/memory_hotplug.c 2012-06-26 13:44:37.069955820 +0900
@@ -661,7 +661,11 @@ EXPORT_SYMBOL_GPL(add_memory);

int remove_memory(int nid, u64 start, u64 size)
{
- return -EBUSY;
+ lock_memory_hotplug();
+ /* remove memmap entry */
+ firmware_map_remove(start, start + size, "System RAM");
+ unlock_memory_hotplug();
+ return 0;

}
EXPORT_SYMBOL_GPL(remove_memory);
Index: linux-3.5-rc4/include/linux/firmware-map.h
===================================================================
--- linux-3.5-rc4.orig/include/linux/firmware-map.h 2012-06-25 04:53:04.000000000 +0900
+++ linux-3.5-rc4/include/linux/firmware-map.h 2012-06-26 13:44:37.070955807 +0900
@@ -25,6 +25,7 @@

int firmware_map_add_early(u64 start, u64 end, const char *type);
int firmware_map_add_hotplug(u64 start, u64 end, const char *type);
+int firmware_map_remove(u64 start, u64 end, const char *type);

#else /* CONFIG_FIRMWARE_MEMMAP */

@@ -38,6 +39,11 @@ static inline int firmware_map_add_hotpl
return 0;
}

+static inline int firmware_map_remove(u64 start, u64 end, const char *type)
+{
+ return 0;
+}
+
#endif /* CONFIG_FIRMWARE_MEMMAP */

#endif /* _LINUX_FIRMWARE_MAP_H */
Index: linux-3.5-rc4/drivers/firmware/memmap.c
===================================================================
--- linux-3.5-rc4.orig/drivers/firmware/memmap.c 2012-06-25 04:53:04.000000000 +0900
+++ linux-3.5-rc4/drivers/firmware/memmap.c 2012-06-26 13:47:17.606948898 +0900
@@ -123,6 +123,16 @@ static int firmware_map_add_entry(u64 st
return 0;
}

+/**
+ * firmware_map_remove_entry() - Does the real work to remove a firmware
+ * memmap entry.
+ * @entry: removed entry.
+ **/
+static inline void firmware_map_remove_entry(struct firmware_map_entry *entry)
+{
+ list_del(&entry->list);
+}
+
/*
* Add memmap entry on sysfs
*/
@@ -144,6 +154,31 @@ static int add_sysfs_fw_map_entry(struct
return 0;
}

+/*
+ * Remove memmap entry on sysfs
+ */
+static inline void remove_sysfs_fw_map_entry(struct firmware_map_entry *entry)
+{
+ kobject_del(&entry->kobj);
+}
+
+/*
+ * Search memmap entry
+ */
+
+struct firmware_map_entry * __meminit
+find_firmware_map_entry(u64 start, u64 end, const char *type)
+{
+ struct firmware_map_entry *entry;
+
+ list_for_each_entry(entry, &map_entries, list)
+ if ((entry->start == start) && (entry->end == end) &&
+ (!strcmp(entry->type, type)))
+ return entry;
+
+ return NULL;
+}
+
/**
* firmware_map_add_hotplug() - Adds a firmware mapping entry when we do
* memory hotplug.
@@ -196,6 +231,42 @@ int __init firmware_map_add_early(u64 st
return firmware_map_add_entry(start, end, type, entry);
}

+void release_firmware_map_entry(struct firmware_map_entry *entry)
+{
+ /*
+ * FIXME : There is no idea.
+ * How to free the entry which allocated bootmem?
+ */
+}
+
+/**
+ * firmware_map_remove() - remove a firmware mapping entry
+ * @start: Start of the memory range.
+ * @end: End of the memory range (inclusive).
+ * @type: Type of the memory range.
+ *
+ * removes a firmware mapping entry.
+ *
+ * Returns 0 on success, or -EINVAL if no entry.
+ **/
+int __meminit firmware_map_remove(u64 start, u64 end, const char *type)
+{
+ struct firmware_map_entry *entry;
+
+ entry = find_firmware_map_entry(start, end, type);

Hmm, we cannot find the entry easily, because the end can be:
1. start + size
2. start + size - 1

So, We should fix this bug first.

This is not a bug.

start and size arguments of firmware_map_remove() include
acpi_memory_info->{start_addr, length}. And when creating a firmware_map_entry,
the entry is created by acpi_memory_info->{start_addr, length}. So I don't
think that we need care your comment.


+ if (!entry)
+ return -EINVAL;
+
+ /* remove the memmap entry */
+ remove_sysfs_fw_map_entry(entry);
+
+ firmware_map_remove_entry(entry);
+
+ release_firmware_map_entry(entry);

I guess you want to free the memory in the above function. But I think it is
not a good idea to free it here. We should free it when the entry->kobj's kref
is decreased to 0.

Thanks.
I'll update your comment at next version.

Thanks,
Yasuaki Ishimatsu


Thanks
Wen Congyang

+
+ return 0;
+}
+
/*
* Sysfs functions -------------------------------------------------------------
*/

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