Date: Wed, 28 Feb 2001 15:11:02 +0100 From: Anton Berezin <tobez@tobez.org> To: Peter Dufault <dufault@hda.hda.com> Cc: hackers@FreeBSD.ORG Subject: Re: how to actually find out whether data hit the disk? Message-ID: <20010228151102.C29400@heechee.tobez.org> In-Reply-To: <200102281357.f1SDvVW27830@hda.hda.com>; from dufault@hda.hda.com on Wed, Feb 28, 2001 at 08:57:31AM -0500 References: <20010228140749.B29400@heechee.tobez.org> <200102281357.f1SDvVW27830@hda.hda.com>
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On Wed, Feb 28, 2001 at 08:57:31AM -0500, Peter Dufault wrote:
> > I am doing the following, on the partition with softupdates turned on:
> >
> > 1. fd = open("a file", O_CREAT)
> > 2. mmap(fd)
> > 3. sequencial write to mmapped region
> > 4. some other processing
> > 5. munmap
> > 6. unlink
> > 7. close
> >
> > Since this is a supposedly high-perfomance application, I am interested
> > that data do NOT hit the disk. I understand that softupdates do a good
> > job at that. The time taken by step 4 is usually sub-second, but
> > sometimes it can take longer (network delays etc.). The question is -
> > is it possible to actually find out whether data hit the disk or not for
> > a particular run of 1-7?
>
> Answer to your question:
>
> Do an msync with MS_SYNC someplace. Also, use MAP_NOSYNC in
> mmap until 4.3 when Matt Dillon plans to make that the default behavior.
Ahh, no. That's the other way around - I do not *want* it to hit the
disk, but would like to *know* when it nevertheless does.
=Anton.
--
May the tuna salad be with you.
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