On Wed, May 09, 2007 at 12:02:29PM +1000, Nick Piggin wrote:
> BTW, we _really_ should be doing RCU properly in slob, because you
> technically can't noop RCU on UP (even though the current users may be
> safe...).
Thanks. Hugh was pretty convinced it was unneeded:
http://marc.info/?l=linux-mm&m=116413907023393&w=2
And since I didn't care much about the SMP case, I didn't pursue it.
This almost looks reasonable. I think HW_ALIGN | RCU is going to make
it break though:
> + if (unlikely(c->flags & SLAB_DESTROY_BY_RCU))
> + b += sizeof(struct slob_rcu);
> +
That could be dealt with by putting the slob_rcu at the end of the
object and having the RCU helper function use ->size to work backward
to the actual pointer.
> void kmem_cache_free(struct kmem_cache *c, void *b)
> {
> if (c->dtor)
> c->dtor(b, c, 0);
I think if we want RCU to actually work, we want to run ->dtor in
__kmem_cache_free?
> - if (c->size < PAGE_SIZE)
> - slob_free(b, c->size);
> - else
> - free_pages((unsigned long)b, find_order(c->size));
> + if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
> + struct slob_rcu *slob_rcu;
> + b -= sizeof(struct slob_rcu);
> + slob_rcu = b;
> + slob_rcu->size = c->size;
Which means just store c in the header^Wfooter, then we can retrieve the size
and the dtor in the RCU helper.
We might as well add slab_is_available and make the damn thing work on
sparsemem again too.
--
Mathematics is the supreme nostalgia of our time.
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