svn commit: r204132 - in user/kib/vm6/sys: conf dev/md kern sys ufs/ffs ufs/ufs vm

[Kostik Belousov]

On Sun, Feb 21, 2010 at 01:21:10PM +0800, David Xu wrote:
> Konstantin Belousov wrote:
> >Author: kib
> >Date: Sat Feb 20 16:34:42 2010
> >New Revision: 204132
> >URL: http://svn.freebsd.org/changeset/base/204132
> >
> >Log:
> >  Implementation of range locking for i/o and vm i/o.
> >  
> >  First vm_readwrite.c implementation by:	jeff
> >  In collaboration with:	pho
> The range locking is confusing, if there are thread A,B and C,
> if A reads range 0-100, B writes range 0-100, C reads 200-300,
> why should C waits before B is guaranteed ? C should be able to freely
> read its data.

I was very conservative. My main goal was to grant range locks to the
threads in the order of arrival. This implicitely avoids any starvation
as a consequence.

Implementation in the kern_rangelock.c is temporal anyway, since it
suffers from the same scalability issues as old sx/lockmgr due to
the use of interlock.
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