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

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Date:	Tue, 27 Mar 2007 10:03:41 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	akpm@...ux-foundation.org
CC:	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch resend v4] update ctime and mtime for mmaped write

> > > There is surely no need to duplicate all that.
> > 
> > Yeah, we could teach generic_writepages() to conditionally not submit
> > for io just test/clear pte dirtyness.
> > 
> > Maybe that would be somewhat cleaner, dunno.
> > 
> > Then there are the ram backed filesystems, which don't have dirty
> > accounting and radix trees, and for which this pte walking is still
> > needed to provide semantics consistent with normal filesystems.
> 
> hm.
> 
> I don't know how important all this is, really - we've had this bug for
> ever and presumably we've already trained everyone to work around it.
> 
> What usage scenarios are people actually hurting from?  Is there anything
> interesting in the mysterious Novell Bugzilla #206431?

That's just a failing LTP testcase, not quite real life ;)

But Peter Staubach says a RH custumer has files written thorugh mmap,
which are not being backed up.

> Perhaps we can get away with doing something half-assed which covers most
> requirements...

OK.  At least I can split the patch into two half asses.

The big question is tmpfs and friends.  Those won't get any timestamp
update without additional page table walking.

Miklos
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