Subject: Re: [RFC PATCH v2 4/13] memory-hotplug : remove /sys/firmware/memmap/X sysfs

From: Wen Congyang <[email-masked]>
Date: Wed, 04 Jul 2012 13:08:44 +0800

At 07/04/2012 12:45 PM, Yasuaki Ishimatsu Wrote:
> Hi Wen,
> 
> 2012/07/03 15:35, Wen Congyang wrote:
>> At 07/03/2012 01:56 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: David Rientjes <[email-masked]>
>>> CC: Jiang Liu <[email-masked]>
>>> CC: Len Brown <[email-masked]>
>>> CC: Benjamin Herrenschmidt <[email-masked]>
>>> CC: Paul Mackerras <[email-masked]>
>>> CC: Christoph Lameter <[email-masked]>
>>> Cc: Minchan Kim <[email-masked]>
>>> CC: Andrew Morton <[email-masked]>
>>> CC: KOSAKI Motohiro <[email-masked]>
>>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>>
>>> ---
>>>   drivers/firmware/memmap.c    |   70 +++++++++++++++++++++++++++++++++++++++++++
>>>   include/linux/firmware-map.h |    6 +++
>>>   mm/memory_hotplug.c          |    6 +++
>>>   3 files changed, 81 insertions(+), 1 deletion(-)
>>>
>>> Index: linux-3.5-rc4/mm/memory_hotplug.c
>>> ===================================================================
>>> --- linux-3.5-rc4.orig/mm/memory_hotplug.c	2012-07-03 14:22:00.190240794 +0900
>>> +++ linux-3.5-rc4/mm/memory_hotplug.c	2012-07-03 14:22:03.549198802 +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 - 1, "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	2012-07-03 14:21:45.766421116 +0900
>>> +++ linux-3.5-rc4/include/linux/firmware-map.h	2012-07-03 14:22:03.550198789 +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	2012-07-03 14:21:45.761421180 +0900
>>> +++ linux-3.5-rc4/drivers/firmware/memmap.c	2012-07-03 14:22:03.569198549 +0900
>>> @@ -79,7 +79,16 @@ static const struct sysfs_ops memmap_att
>>>   	.show = memmap_attr_show,
>>>   };
>>>
>>> +static void release_firmware_map_entry(struct kobject *kobj)
>>> +{
>>> +	/*
>>> +	 * FIXME : There is no idea.
>>> +	 *         How to free the entry which allocated bootmem?
>>> +	 */
>>
>> I find a function free_bootmem(), but I am not sure whether it can work here.
> 
> It cannot work here.
> 
>> Another problem: how to check whether the entry uses bootmem?
> 
> When firmware_map_entry is allocated by kzalloc(), the page has PG_slab.

This is not true. In my test, I find the page does not have PG_slab sometimes.

Thanks
Wen Congyang.

> So we can check whether the entry was allocated by bootmem or not.
> If the eantry was allocated by kzalloc(), we can free the entry by kfree().
> But if the entry was allocated by bootmem, we have no way to free the entry.
> 
> Thanks,
> Yasuaki Ishimatsu
> 
>>
>> Thanks
>> Wen Congyang
>>
>>> +}
>>> +
>>>   static struct kobj_type memmap_ktype = {
>>> +	.release	= release_firmware_map_entry,
>>>   	.sysfs_ops	= &memmap_attr_ops,
>>>   	.default_attrs	= def_attrs,
>>>   };
>>> @@ -123,6 +132,16 @@ 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 +163,31 @@ 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_put(&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 +240,32 @@ int __init firmware_map_add_early(u64 st
>>>   	return firmware_map_add_entry(start, end, type, entry);
>>>   }
>>>
>>> +/**
>>> + * 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);
>>> +	if (!entry)
>>> +		return -EINVAL;
>>> +
>>> +	/* remove the memmap entry */
>>> +	remove_sysfs_fw_map_entry(entry);
>>> +
>>> +	firmware_map_remove_entry(entry);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>>   /*
>>>    * Sysfs functions -------------------------------------------------------------
>>>    */
>>>
>>> --
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>>
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> 
> 
> 
>