Re: [PATCH] Containment measures for slab objects on scatter gather lists

[David Miller <davem@davemloft.net>]

From: Andrew Morton <akpm@linux-foundation.org>
Date: Thu, 28 Jun 2007 22:24:24 -0700

> So what happens when two quite different threads of control are doing
> IO against two hunks of kmalloced memory which happen to come from the same
> page?  Either some (kernel-wide) locking is needed, or that pageframe needs
> to be treated as readonly?

Or you put an atomic_t at the beginning or tail of every SLAB
object.  It's a space cost not a runtime cost for the common
case which is:

	smp_rmb();
	if (atomic_read(&slab_obj->count) == 1)
		really_free_it();
	else if (atomic_dec_and_test(...))

Note I don't like this variant either. :)

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