linux-kernel - Re: Concerning a post that you made about expandable anonymous shared mappings

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Date:	Tue, 10 Jul 2007 21:10:11 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	William Tambe <tambewilliam@...il.com>
cc:	Stas Sergeev <stsp@...et.ru>,
	"Rohland, Hans-Christoph" <hans-christoph.rohland@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: Concerning a post that you made about expandable anonymous shared
 mappings

On Mon, 9 Jul 2007, William Tambe wrote:
> Hugh Dickins wrote:
> > 
> > I've come right around to your original view, Stas, and William's:
> > if that mmap creates such an object, then the expanding mremap really
> > ought to be useful, and allow the underlying object to be expanded.
> > The shared anonymous object is already anomalous: expanding it on
> > fault makes it more consistent with its own nature, not less.
> > ...
> > Here's a patch against 2.6.22-rc7: would you, Stas, put your
> > Signed-off-by into this, and accept authorship - although I'm
> > sending this back to you, it's very much your idea, and only
> > trivially modified from your three-year-old patch by me.  If
> > you're agreeable, I can then forward it or its shmem_zero_fault
> > equivalent to Andrew when we see which way 2.6.23 is going.
>... 
> Will this patch be added to stable versions of the linux kernel?
> Please let me know.

I confess that the lukewarm response from Stas cooled my enthusiasm,
and left me feeling that perhaps I'm an idiot to be adding such a
feature so many years too late; and my old caution about the way
a child could use up memory not freed on child's exit, unknown to
parent, returned to haunt me.  That could be documented for new
usages, but I just don't know what usages are already out there,
and fear I'd be introducing an exploit.

It most certainly will not be added to a stable version of the
linux kernel, if by that you mean 2.6.22.N or 2.6.21.N etc.
Though it can be viewed as a bugfix, the patch as it stands
seems in danger of introducing its own bug, and it's just too
much of a feature to be suitable for a -stable release.

But more probably you meant, will it be in 2.6.23 or 2.6.24?
Sorry to be such a vacillatiing wimp, but I don't know.
How well are you managing with the shm_open approach?

Hugh
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