linux-kernel - Re: [patch resend v4] update ctime and mtime for mmaped write

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Date:	28 Mar 2007 05:50:14 -0400
From:	linux@...izon.com
To:	nickpiggin@...oo.com.au
Cc:	akpm@...ux-foundation.org, linux@...izon.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, miklos@...redi.hu
Subject: Re: [patch resend v4] update ctime and mtime for mmaped write

> But if you didn't notice until now, then the current implementation
> must be pretty reasonable for you use as well.

Oh, I definitely noticed.  As soon as I tried to port my application
to 2.6, it broke - as evidenced by my complaints last year.  The
current solution is simple - since it's running on dedicated boxes,
leave them on 2.4.

I've now got the hint on how to make it work on 2.6 (sync_file_range()),
so I can try again.  But the pressure to upgrade is not strong, so it
might be a while.

You may recall, this subthread started when I responding to "the
only reason to use msync(MS_ASYNC) is to update timestamps" with a
counterexample.  I still think the purpose of the call is a hint to the
kernel that writing to the specified page(s) is complete and now would be
a good time to clean them.  Which has very little to do with timestamps.

Now, my application, which leaves less than a second between the MS_ASYNC
and a subsequent MS_SYNC to check whether it's done, broke, but I can
imagine similar cases where MS_ASYNC would remain a useful hint to reduce
the sort of memory hogging generally associated with "dd if=/dev/zero"
type operations.

Reading between the lines of the standard, that seems (to me, at least)
to obviously be the intended purpose of msync(MS_ASYNC).  I wonder if
there's any historical documentation describing the original intent
behind creating the call.
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