Re: [PATCH]updated ipc lock patch

[Rusty Russell]

In message <20021029013059.A13287@dikhow> you write:
> Hi Rusty,
> 
> I am pathologically late in catching up lkml, so if I missed some
> context here, I apologize in advance. I have just started looking
> at mm6 ipc code and I want to point out a few things.

That's OK, I'm still 1500 behind 8(

	If all current uses are embedded, can we remove the "void
*arg" and reduce the size of struct rcu_head by 25%?  Users can always
embed it in their own struct which has a "void *arg", but if that's
the uncommon case, it'd be nice to slim it a little.

	It'd also be nice to change the double linked list to a single
too: as far as I can tell the only issue is the list_add_tail in
call_rcu(): how important is this ordering?  It can be done by keeping
a head as well as a tail pointer if required.

I'd be happy to prepare a patch, to avoid more complaints of bloat 8)

> That said, it seems that Ming/Hugh's patch does allocate
> the rcu_head at the time of *growing* the array. It is just
> that they allocate it for the freeing array rather than the
> allocated array. I don't see how this is semantically different
> from clubbing the two allocations other than the fact that
> smaller number of allocation calls would likely reduce the
> likelyhood of allocation failures.

We must be looking at different variants of the patch.  This one does:
IPC_RMID -> freeary() -> ipc_rcu_free -> kmalloc.

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.