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

From: Yasuaki Ishimatsu <[email-masked]>
Date: Wed, 4 Jul 2012 14:52:30 +0900

Hi Wen,

2012/07/04 14:08, Wen Congyang wrote:
> 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.

I think that it depends on the allocated size. firmware_map_entry size is
smaller than PAGE_SIZE. So the page has PG_Slab.

Thanks,
Yasuaki Ishimatsu

> 
> 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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>>
>>
>>
>>
> 
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