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

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Date:	Thu, 23 Dec 2010 10:00:20 +0800
From:	Shaohui Zheng <shaohui.zheng@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	shaohui.zheng@...el.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...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 Wed, Dec 22, 2010 at 04:27:36PM -0800, Andrew Morton wrote:
> 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.
> 

Yes, It is a my habit to initialize variable when define it. I will check them 
one by one.

> > +	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;
> 
> 

An explicit typecast looks much better.

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

We ignored the warning for function simple_strtoull in the whole patchset.
We will solve it one by one.

> > +	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?
> 

Yes, I added the usage information when create the add_memory entry, it seems
that I should also add comment here.

/* 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 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.
> 

Totally agree. I see that the simliar call on debugfs_create_dir. For the failure,
most of them assume ENOMEM, some of them assume as EINVAL.

> > +	/* 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".
> 

Good catching.

> > +{
> > +	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;
> >  }
> >  
> >
> > ...
> >

-- 
Thanks & Regards,
Shaohui

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