Re: [PATCH 2/4] Convert epoll to a bitlock

Andrew Morton
2009-02-03T22:06:58Z

On Tue, 03 Feb 2009 22:55:26 +0100
Eric Dumazet <dada1@cosmosbay.com> wrote:

> Andrew Morton a __crit :
> > On Mon, 2 Feb 2009 11:20:09 -0700
> > Jonathan Corbet <corbet@lwn.net> wrote:
> >
> >> Matt Mackall suggested converting epoll's ep_lock to a bitlock as a way of
> >> saving space in struct file. This patch makes that change.
> >
> > hrm. bit_spin_lock() makes people upset (large penguiny people). iirc
> > it doesn't have all the correct/well-understood memory/compiler
> > ordering semantics which spinlocks have. And lockdep doesn't know about
> > it.
> >
>
> In a previous attempt (2005), I suggested using a single global lock.
>
> http://search.luky.org/linux-kernel.2005/msg50862.html

ok..

> Probably an array of hashed spinlocks would be more than enough.
>

yes, f_ep_lock is a teeny innermost lock. Perhaps using
f->f_dentry->d_inode->i_lock would be a decent speed/space compromise.