linux-kernel - Re: [7/7,v8] NUMA Hotplug Emulator: Implement per-node add

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Message-ID: <alpine.DEB.2.00.1012091325530.13564@chino.kir.corp.google.com>
Date:	Thu, 9 Dec 2010 13:29:28 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohui Zheng <shaohui.zheng@...el.com>
cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com, gregkh@...e.de,
	shaohui.zheng@...ux.intel.com
Subject: Re: [7/7,v8] NUMA Hotplug Emulator: Implement per-node add_memory
 debugfs interface

On Thu, 9 Dec 2010, Shaohui Zheng wrote:

> > I don't think you should be using memparse() to support this type of 
> > interface, the standard way of writing memory locations is by writing 
> > address in hex as the first example does.  The idea is to not try to make 
> > things simpler by introducing multiple ways of doing the same thing but 
> > rather to standardize on a single interface.
> 
> Undoubtedly, A hex is the best way to represent a physical address. If we use
> memparse function, we can use the much simpler way to represent an address,
> it is not the offical way, but it takes many conveniences if we just want to 
> to some simple test.
> 

Testing code should be removed from the patch prior to proposal.

> When we reserce memory, we use mempasre to parse the mem=XXX parameter, we can
> avoid the complicated translation when we add memory thru the add_memory interface,
> how about still use the memparse here? but remove it from the document since it is
> just for some simple testing. 
> 

We really don't want a public interface to have undocumented behavior, so 
it would be much better to retain the documentation if you choose to keep 
the memparse().  I disagree that converting the mem= parameter to hex is 
"complicated," however, so I'd prefer that the interface is similar to 
that of add_node.

> > > +	printk(KERN_INFO "Add a memory section to node: %d.\n", nid);
> > > +	phys_addr = memparse(buf, NULL);
> > > +	ret = add_memory(nid, phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);
> > 
> > Does the add_memory() call handle memoryless nodes such that they 
> > appropriately transition to N_HIGH_MEMORY when memory is added?
> 
> For memoryless nodes, it will cause OOM issue on old kernel version, but now
> memoryless node is already supported, and the test result matches it well. The
> emulator is a tool to reproduce the OOM issue in eraly kernel.
> 

That doesn't address the question.  My question is whether or not adding 
memory to a memoryless node in this way transitions its state to 
N_HIGH_MEMORY in the VM?
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