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    SubjectRe: + fix-spellings-of-slab-allocator-section-in-init-kconfig.patch added to -mm tree
    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:

    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

    > - 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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