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

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Date:	Tue, 10 Jul 2007 15:55:30 -0500
From:	William Tambe <tambewilliam@...il.com>
To:	Hugh Dickins <hugh@...itas.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



Hugh Dickins wrote:
> 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
> 

I understand your concern. But since I am working on a dynamic memory 
management code that I wish to use with other projects that I have, I 
didn't find appropriate to use shm_open.

In fact there is a name associated with the shared memory requested with 
shm_open, so that it can be mmap(ed) in another process. And I do not 
wish to have it accessible by any other process, unless I choose to do so.

shm_open is great, but it doesn't quite fit my needs.
And I think remap(ing) ANONYMOUS memory kind of make a lot of things easier.

Can that feature be added at least to release candidates series so that 
everybody can try it and see how well it does?

Sincerely,
William Tambe
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