Date: Fri, 9 Feb 2001 10:14:21 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: freebsd-current@FreeBSD.ORG Cc: Dag-Erling Smorgrav <des@ofug.org>, Julian Elischer <julian@elischer.org>, Josef Karthauser <joe@tao.org.uk>, Robert Watson <rwatson@FreeBSD.ORG>, Brian Somers <brian@Awfulhak.org>, Bruce Evans <bde@zeta.org.au>, freebsd-current@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: What's changed recently with vmware/linuxemu/file I/O Message-ID: <14980.2381.849005.313177@grasshopper.cs.duke.edu> In-Reply-To: <14979.29437.518299.842853@grasshopper.cs.duke.edu> References: <xzpsnlqmh0o.fsf@flood.ping.uio.no> <Pine.NEB.3.96L.1010207220443.19807J-100000@fledge.watson.org> <20010208113519.A789@tao.org.uk> <3A828C2C.F7CDA809@elischer.org> <xzp4ry5gve0.fsf@flood.ping.uio.no> <14979.29437.518299.842853@grasshopper.cs.duke.edu>
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Andrew Gallatin writes: > > Dag-Erling Smorgrav writes: > > Julian Elischer <julian@elischer.org> writes: > > > I believe that vmware mmaps a region of memory and then somehow syncs > > > it to disk. (It is certainly doing something like it here). > > > > Theory: VMWare mmaps a region of memory corresponding to the virtual > > machine's "physical" RAM, then touches every page during startup. > > Unless some form of clustering is done, this causes 16384 write > > operations for a 64 MB virtual machine... > > > > Pretty much. But the issue is that this should never hit the disk > unless we're under memory pressure because it is mapped MAP_NOSYNC > (actually the file is unlinked prior to the mmap() and a heuristic in > vm_mmap() detects this and sets MAP_NOSYNC). I take it back. At least with the latest version of vmware, it is apparently not mapped MAP_NOSYNC. I think they've moved from mmap'ing a file in $TMPDIR to just using the CONFIG.std save/resume file. Perhaps this is only if you have resumed from a suspended state... I haven't checked that out yet. At any rate, hacking linux_mmap to ad MAP_NOSYNC to mmaped files, in combination with yesterdays patch, appears to improve perf. considerably. Drew ------------------------------------------------------------------------------ Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin Duke University Email: gallatin@cs.duke.edu Department of Computer Science Phone: (919) 660-6590 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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