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    SubjectRe: [PATCH V4 1/1] rcu: introduce kfree_rcu()
    On Tue, Mar 15, 2011 at 02:07:24PM +0100, Arnd Bergmann wrote:
    > On Tuesday 15 March 2011, Paul E. McKenney wrote:
    > > And it makes use of statically allocated structures a bit clunky.
    > How do statically allocated structures relate to this? I would
    > expect that you never call kfree_rcu on them, so it shouldn't
    > matter.
    > > Yet another approach is to use the low-order bit of the rcu_head pointer,
    > > given that the rcu_head structure does have to be aligned. If this bit
    > > is set, then the function pointer could be interpreted as an offset.
    > > This approach might also allow a slab_free_rcu() to be constructed, given
    > > that the full 32 bits of the function pointer would be available.
    > > For example, if the upper 16 bits are zero, the low-order 16 bits are
    > > the offset. If the upper 16 bits are 0x1, then the low-order 16 bits
    > > might be an index that selects the desired slab cache.
    > This solution sounds like a clear improvement over the patch that Lai
    > Jiangshan posted, without any downsides.

    Except that I was forgetting that we don't really have any way to stop
    people from handing us misaligned rcu_head structures -- that topic came
    up last time as well. Or were the people mentioning that possibility
    being overly paranoid?

    Thanx, Paul

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