linux-kernel - Re: [7/7, v9] NUMA Hotplug Emulator: Implement per-node add

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Message-Id: <20101222162736.e51d2e18.akpm@linux-foundation.org>
Date:	Wed, 22 Dec 2010 16:27:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	shaohui.zheng@...el.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	haicheng.li@...ux.intel.com, lethal@...ux-sh.org,
	ak@...ux.intel.com, shaohui.zheng@...ux.intel.com,
	rientjes@...gle.com, dave@...ux.vnet.ibm.com, gregkh@...e.de,
	Haicheng Li <haicheng.li@...el.com>
Subject: Re: [7/7, v9] NUMA Hotplug Emulator: Implement per-node add_memory
 debugfs interface

On Fri, 10 Dec 2010 15:31:26 +0800
shaohui.zheng@...el.com wrote:

> From:  Shaohui Zheng <shaohui.zheng@...el.com>
> 
> Add add_memory interface to support to memory hotplug emulation for each online
> node under debugfs. The reserved memory can be added into desired node with
> this interface.
> 
> The layout on debugfs:
> 	mem_hotplug/node0/add_memory
> 	mem_hotplug/node1/add_memory
> 	mem_hotplug/node2/add_memory
> 	...
> 
> Add a memory section(128M) to node 3(boots with mem=1024m)
> 
> 	echo 0x40000000 > mem_hotplug/node3/add_memory
> 
>
> ...
>
> +#ifdef CONFIG_ARCH_MEMORY_PROBE
> +
> +static ssize_t add_memory_store(struct file *file, const char __user *buf,
> +				size_t count, loff_t *ppos)
> +{
> +	u64 phys_addr = 0;

Even more unneeded initalisation.

Please check the whole patchset for this.  It's bad because it can
sometimes generate more code and because it can sometimes hide bugs by
suppressing used-uninitialsied warnings.

> +	int nid = file->private_data - NULL;

Well that was sneaky.

It would be more conventional to just use the typecast:

	int nid = (long)file->private_data;


> +	int ret;
> +
> +	printk(KERN_INFO "Add a memory section to node: %d.\n", nid);
> +	phys_addr = simple_strtoull(buf, NULL, 0);

checkpatch

> +	ret = add_memory(nid, phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);
> +	if (ret)
> +		count = ret;
> +
> +	return count;
> +}
> +
> +static int add_memory_open(struct inode *inode, struct file *file)
> +{
> +	file->private_data = inode->i_private;

Was this usage of i_private and private_data documented in comments
somewhere?

> +	return 0;
> +}
> +
> +static const struct file_operations add_memory_file_ops = {
> +	.open		= add_memory_open,
> +	.write		= add_memory_store,
> +	.llseek		= generic_file_llseek,
> +};
> +
> +/*
> + * Create add_memory debugfs entry under specified node
> + */
> +static int debugfs_create_add_memory_entry(int nid)
> +{
> +	char buf[32];
> +	static struct dentry *node_debug_root;
> +
> +	snprintf(buf, sizeof(buf), "node%d", nid);
> +	node_debug_root = debugfs_create_dir(buf, memhp_debug_root);
> +	if (!node_debug_root)
> +		return -ENOMEM;

hm, debugfs_create_dir() was poorly designed - it should return an
ERR_PTR() so callers don't need to assume ENOMEM, which may be incorrect.

> +	/* the nid information was represented by the offset of pointer(NULL+nid) */
> +	if (!debugfs_create_file("add_memory", S_IWUSR, node_debug_root,
> +			NULL + nid, &add_memory_file_ops))
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +static int __init memory_debug_init(void)
> +{
> +	int nid;
> +
> +	if (!memhp_debug_root)
> +		memhp_debug_root = debugfs_create_dir("mem_hotplug", NULL);
> +	if (!memhp_debug_root)
> +		return -ENOMEM;
> +
> +	for_each_online_node(nid)
> +		 debugfs_create_add_memory_entry(nid);
> +
> +	return 0;
> +}
> +
> +module_init(memory_debug_init);
> +#else
> +static debugfs_create_add_memory_entry(int nid)

"static int".

> +{
> +	return 0;
> +}
> +#endif /* CONFIG_ARCH_MEMORY_PROBE */
> +
>  static ssize_t add_node_store(struct file *file, const char __user *buf,
>  				size_t count, loff_t *ppos)
>  {
> @@ -963,6 +1038,8 @@
>  		return -ENOMEM;
>  
>  	ret = add_memory(nid, start, size);
> +
> +	debugfs_create_add_memory_entry(nid);
>  	return ret ? ret : count;
>  }
>  
>
> ...
>

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