Date: Sat, 21 Aug 2004 21:58:00 -0400 From: Brian Fundakowski Feldman <green@FreeBSD.org> To: Alan Cox <alc@cs.rice.edu> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/vm vm_fault.c Message-ID: <20040822015800.GE784@green.homeunix.org> In-Reply-To: <20040822001559.GG9106@cs.rice.edu> References: <200408211920.i7LJKLlA088634@repoman.freebsd.org> <20040821225939.GA784@green.homeunix.org> <20040821233134.GF9106@cs.rice.edu> <20040821234116.GC784@green.homeunix.org> <20040822001559.GG9106@cs.rice.edu>
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On Sat, Aug 21, 2004 at 07:15:59PM -0500, Alan Cox wrote: > On Sat, Aug 21, 2004 at 07:41:16PM -0400, Brian Fundakowski Feldman wrote: > > On Sat, Aug 21, 2004 at 06:31:34PM -0500, Alan Cox wrote: > > > On Sat, Aug 21, 2004 at 06:59:39PM -0400, Brian Fundakowski Feldman wrote: > > > > On Sat, Aug 21, 2004 at 07:20:21PM +0000, Alan Cox wrote: > > > > > alc 2004-08-21 19:20:21 UTC > > > > > > > > > > FreeBSD src repository > > > > > > > > > > Modified files: > > > > > sys/vm vm_fault.c > > > > > Log: > > > > > Further reduce the use of Giant by vm_fault(): Giant is held only when > > > > > manipulating a vnode, e.g., calling vput(). This reduces contention for > > > > > Giant during many copy-on-write faults, resulting in some additional > > > > > speedup on SMPs. > > > > > > > > > > Note: debug_mpsafevm must be enabled for this optimization to take effect. > > > > > > > > This is very broken. See included first attempt at fixing it without > > > > regard for actually trying to reimplement debug.mpsafenet for vnodes. > > > > > > > > > > Can you please explain what is broken? > > > > #1. Lock order reversal. Giant is acquired after the map read lock. > > No, that is the order it has been in for months. The other functions > that acquire a map lock and Giant do the same. Giant can never be acquired after another lock has been acquired :-( -- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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