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

[Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>]

On Tue, 03 Feb 2009 22:55:26 +0100
Eric Dumazet <dada1-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org> wrote:

> Andrew Morton a __crit :
> > On Mon,  2 Feb 2009 11:20:09 -0700
> > Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org> 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.


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