Re: [patch 6/7] mm: lockless pagecache

Nick Piggin
2005-08-12T04:04:45Z

On Thu, 2005-08-11 at 18:49 -0700, Paul E. McKenney wrote:
> On Thu, Aug 11, 2005 at 10:28:04PM +1000, Nick Piggin wrote:
> > 6/7
> >
> > --
> > SUSE Labs, Novell Inc.
> >
>
> > Use the speculative get_page and the lockless radix tree lookups
> > to introduce lockless page cache lookups (ie. no mapping->tree_lock).
> >
> > The only atomicity changes this should introduce is the use of a
> > non atomic pagevec lookup for truncate, however what atomicity
> > guarantees there were are probably not too useful anyway.
>
> I don't understand the placement of the rcu_read_lock() and
> rcu_read_unlock() calls. Again, possibly because I don't understand
> the overall algorithm yet. And again, search for blank lines.
>

I hope I gave a satisfactory answer to this in the last email. If
not, let me know what I've missed...

Indeed you are right that we could push all the RCU locking down
into the radix tree lookups in the places you mention _if_ we
didn't rely on lookups returning radix tree *slots*.

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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