Date: Tue, 3 Aug 2004 12:56:15 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Stephan Uphoff <ups@tree.com> Cc: cvs-src@FreeBSD.org Subject: Re: cvs commit: src/sys/vm vm_map.c vm_map.h Message-ID: <200408031256.15886.jhb@FreeBSD.org> In-Reply-To: <200408030258.i732wAfY098990@palm.tree.com> References: <200408030258.i732wAfY098990@palm.tree.com>
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On Monday 02 August 2004 10:58 pm, Stephan Uphoff wrote: > John Baldwin wrote: > > On Friday 30 July 2004 12:06 pm, Brian Fundakowski Feldman wrote: > > > On Fri, Jul 30, 2004 at 09:10:28AM +0000, Maxime Henrion wrote: > > > > mux 2004-07-30 09:10:28 UTC > > > > > > > > FreeBSD src repository > > > > > > > > Modified files: > > > > sys/vm vm_map.c vm_map.h > > > > Log: > > > > Get rid of another lockmgr(9) consumer by using sx locks for the > > > > user maps. We always acquire the sx lock exclusively here, but we > > > > can't use a mutex because we want to be able to sleep while holding > > > > the lock. This is completely equivalent to what we were doing with > > > > the lockmgr(9) locks before. > > > > > > Not that I don't think it's worth doing in general, but is there a > > > comparison anyone has done between speeds of sx and lockmgr? > > > > Speed aside, when allproc_lock and proctree_lock were lockmgr locks > > (before sx was implemented), my SMP machines routinely locked up and when > > I looked at things in the debugger it seemed that no one held > > allproc_lock but several processes were blocked on it. Quite frankly, I > > don't trust lockmgr()'s implementation. > > Since the vfs layer forces me to use the lockmgr you scared me into > taking a look. > And yes there is a bug in the current implementation. (kern/69934). Good catch! Unfortunately, the problems I was seeing above involved locks that didn't use upgrade or downgrade. :( I've pondered taking an axe to all of lockmgr and just rewriting it from scratch to use mutexes and cv's like sx. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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