On Fri, 18 Jan 2013, 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

We can avoid the above scenario by doing a cpu local fetch.

i.e.
`	tid = this_cpu_read(s->cpu_slab->tid);

quoted

			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>

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!

Well, the consequence would be that an object from another node than
desired will be allocated. Not that severe of an issue.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>