linux-kernel - Re: mtime updates for mmapped files.

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Message-ID: <4df4ef0c0801160322j31645554oa6faec5cca64509d@mail.gmail.com>
Date:	Wed, 16 Jan 2008 14:22:49 +0300
From:	"Anton Salikhmetov" <salikhmetov@...il.com>
To:	"Rogier Wolff" <R.E.Wolff@...wizard.nl>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: mtime updates for mmapped files.

2008/1/16, Rogier Wolff <R.E.Wolff@...wizard.nl>:
>
> Hi,
>
> I  wrote a small app yesterday that updates a file by mmapping the
> file (RW), changing the thing around, and then exiting.
>
> This did not trigger a change in the mtime of the file. Thus rsync
> didn't pick up that the file had changed.
>
> I understand that tracking every change to a RW mmapped file is
> costly, and thus unfeasable, but shouldn't then the close cause a
> mtime update?
>
> The server where this happened is running 2.6.21, so my apologies if
> this has already been corrected.

Unfortunately, this issue has not been fully fixed yet.

My last attempt (http://lkml.org/lkml/2008/1/15/202) to solve
this problem has a couple of drawbacks:

1) calling a possibly sleeping function from atomic context -
I've already corrected this;

2) there's a very special case with retouching the memory-mapped data
after a call to msync() with MS_ASYNC.

I'm still working on the latter case, but I guess that I have found a solution.

If you badly need a quick fix, I can send my working unreleased patch to you.
I reckon that your particular problem will be fixed by this patch.
Let me know if you want that.

However, if your application calls msync() with the MS_ASYNC flag,
it's better to wait a little bit more - I'll release the next version
of my solution
shortly.

>
>         Roger.
>
> --
> ** R.E.Wolff@...Wizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
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