From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Mackall Subject: Re: [PATCH 2/4] Convert epoll to a bitlock Date: Tue, 03 Feb 2009 16:22:02 -0600 Message-ID: <1233699722.3243.127.camel@calx> References: <1233598811-6871-1-git-send-email-corbet@lwn.net> <1233598811-6871-3-git-send-email-corbet@lwn.net> <20090203133942.2ecec281.akpm@linux-foundation.org> <4988BD4E.8080206@cosmosbay.com> <20090203140543.6e915f97.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090203140543.6e915f97.akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Morton Cc: Eric Dumazet , corbet-T1hC0tSOHrs@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org, oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org, davidel-AhlLAIvw+VEjIGhXcJzhZg@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org List-Id: linux-api@vger.kernel.org On Tue, 2009-02-03 at 14:05 -0800, Andrew Morton wrote: > On Tue, 03 Feb 2009 22:55:26 +0100 > Eric Dumazet wrote: > > > Andrew Morton a __crit : > > > On Mon, 2 Feb 2009 11:20:09 -0700 > > > Jonathan Corbet 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. That seems eminently reasonable. But that re-opens the question of what to do about poor Jon's quest. I got confused halfway through as he went from using a global fasync spinlock to a non-locked but atomic flag bit. Not sure why using a per-file or per-inode lock doesn't work for the fasync code. -- http://selenic.com : development and support for Mercurial and Linux -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html