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    SubjectRe: [PATCH] slub: fix slab_pad_check()
    On Fri, Sep 04, 2009 at 11:42:17AM -0400, Christoph Lameter wrote:
    > On Thu, 3 Sep 2009, Paul E. McKenney wrote:
    >
    > > If it were the user of the slab who was invoking some variant of
    > > call_rcu(), then I would agree with you.
    >
    > The user already has to deal with it as explained by Eric.

    I didn't read his email that way. Perhaps I misinterpreted it.

    > > However, call_rcu() is instead being invoked by the slab itself in the
    > > case of SLAB_DESTROY_BY_RCU, so that there is no variation in usage.
    > > Requiring that the user call rcu_barrier() is asking for subtle bugs.
    > > Therefore, the best approach is to have kmem_cache_destroy() handle
    > > the RCU cleanup, given that this cleanup is for actions taken by
    > > kmem_cache_free(), not by the user.
    >
    > The user already has to properly handle barriers and rcu logic in order to
    > use objects handled with RCU properly. Moreover the user even has to check
    > that the object is not suddenly checked under it. Its already complex.

    mm/slab.c has had RCU calls since 2.6.9, so this is not new.

    > Guess we are doing this ... Sigh. Are you going to add support other rcu
    > versions to slab as well as time permits and as the need arises? Should
    > we add you as a maintainer? ;-)

    I don't see any point in adding anything resembling SLAB_DESTROY_BY_RCU_BH,
    SLAB_DESTROY_BY_RCU_SCHED, or SLAB_DESTROY_BY_SRCU unless and until
    someone needs it. And I most especially don't see the point of adding
    (say) SLAB_DESTROY_BY_RCU_BH_SCHED until someone convinces me of the
    need for it. I would prefer to put the energy into further streamlining
    the underlying RCU implementation, maybe someday collapsing RCU-BH back
    into RCU. ;-)

    We have gotten along fine with only SLAB_DESTROY_BY_RCU for almost
    five years, so I think we are plenty fine with what we have. So, as
    you say, "as the need arises".

    I don't see any more need to add me as maintainer of slab and friends
    than of btrfs, netfilter, selinux, decnet, afs, wireless, or any of a
    number of other subsystems that use RCU.

    Thanx, Paul


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