From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 2/3] dio: scale unaligned IO tracking via multiple lists Date: Tue, 9 Nov 2010 10:12:56 +1100 Message-ID: <20101108231256.GS2715@dastard> References: <1289202023-15102-1-git-send-email-david@fromorbit.com> <1289202023-15102-3-git-send-email-david@fromorbit.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Jeff Moyer Return-path: Received: from bld-mail19.adl2.internode.on.net ([150.101.137.104]:44602 "EHLO mail.internode.on.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1749667Ab0KHXNC (ORCPT ); Mon, 8 Nov 2010 18:13:02 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Nov 08, 2010 at 10:36:06AM -0500, Jeff Moyer wrote: > Dave Chinner writes: > > > From: Dave Chinner > > > > To avoid concerns that a single list and lock tracking the unaligned > > IOs will not scale appropriately, create multiple lists and locks > > and chose them by hashing the unaligned block being zeroed. > > > > Signed-off-by: Dave Chinner > > --- > > fs/direct-io.c | 49 ++++++++++++++++++++++++++++++++++++------------- > > 1 files changed, 36 insertions(+), 13 deletions(-) > > > > diff --git a/fs/direct-io.c b/fs/direct-io.c > > index 1a69efd..353ac52 100644 > > --- a/fs/direct-io.c > > +++ b/fs/direct-io.c > > @@ -152,8 +152,28 @@ struct dio_zero_block { > > atomic_t ref; /* reference count */ > > }; > > > > -static DEFINE_SPINLOCK(dio_zero_block_lock); > > -static LIST_HEAD(dio_zero_block_list); > > +#define DIO_ZERO_BLOCK_NR 37LL > > I'm always curious to know how these numbers are derived. Why 37? It's a prime number large enough to give enough lists to minimise contention whilst providing decent distribution for 8 byte aligned addresses with low overhead. XFS uses the same sort of waitqueue hashing for global IO completion wait queues used by truncation and inode eviction (see xfs_ioend_wait()). Seemed reasonable (and simple!) just to copy that design pattern for another global IO completion wait queue.... Cheers, Dave. -- Dave Chinner david@fromorbit.com