Re: [RFC][PATCH v2] slub: Keep page and object in sync in slab_alloc_node()

On Fri, Jan 18, 2013 at 10:55:01AM -0500, Steven Rostedt wrote:

On Fri, 2013-01-18 at 10:04 -0500, Steven Rostedt wrote:

Just to be more complete:

quoted

	CPU0			CPU1
	----			----

			c = __this_cpu_ptr(s->cpu_slab);
			<migrates to CPU0>

quoted

<cpu fetches c->page>

			<another task>

quoted

			updates c->tid
			updates c->page
			updates c->freelist
<cpu fetches c->tid>
<cpu fetches c->freelist>

  node_match() succeeds even though
    current c->page wont

 <migrates back to CPU 1>

Hello.
I have one stupid question just for curiosity.
Does the processor re-order instructions which load data from same cacheline?

quoted

 this_cpu_cmpxchg_double() only tests
   the object (freelist) and tid, both which
   will match, but the page that was tested
   isn't the right one.

Yes, it's very unlikely, but we are in the business of dealing with the
very unlikely. That's because in our business, the very unlikely is very
likely. Damn, I need to buy a lotto ticket!

-- Steve


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