Re: RFC: Block reservation for hugetlbfs

[Nick Piggin]

David Gibson wrote:
> On Wed, Feb 22, 2006 at 11:38:42AM +1100, Nick Piggin wrote:
>
> > David Gibson wrote:
> >
> > > On Tue, Feb 21, 2006 at 03:18:59PM +1100, Nick Piggin wrote:
> >
> > > > This introduces
> > > > tree_lock(r) -> hugetlb_lock
> > > >
> > > > And we already have
> > > > hugetlb_lock -> lru_lock
> > > >
> > > > So we now have tree_lock(r) -> lru_lock, which would deadlock
> > > > against lru_lock -> tree_lock(w), right?
> > >
> > > > From a quick glance it looks safe, but I'd _really_ rather not
> > >
> > > > introduce something like this.
> > >
> > >
> > > Urg.. good point.  I hadn't even thought of that consequence - I was
> > > more worried about whether I need i_lock or i_mutex to protect my
> > > updates to i_blocks.
> > >
> > > Would hugetlb_lock -> tree_lock(r) be any preferable (I think that's a
> > > possible alternative).
> >
> > Yes I think that should avoid the introduction of new lock dependency.
>
>
> Err... "Yes" appears to contradict the rest of you statement, since my
> suggestion would still introduce a lock dependency, just a different
> one one.  It is not at all obvious to me how to avoid a lock
> dependency entirely.

I mean a new core mm lock depenency (ie. lru_lock -> tree_lock).

But I must have been smoking something last night: for the life
of me I can't see why I thought there was already a hugetlb_lock
-> lru_lock dependency in there...?!

So I retract my statement. What you have there seems OK.


> Also, any thoughts on whether I need i_lock or i_mutex or something
> else would be handy..

I'm not much of an fs guy. How come you don't use i_size?

--
SUSE Labs, Novell Inc.
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