linux-kernel - Re: [RFC][PATCHSET] mremap/mmap mess

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Date:	Wed, 9 Dec 2009 13:46:20 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	David Miller <davem@...emloft.net>, Ollie Wild <aaw@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>, viro@....linux.org.uk,
	linux-arch@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCHSET] mremap/mmap mess

On Wed, Dec 09, 2009 at 11:43:57AM +0000, Hugh Dickins wrote:
> ... my hair ;-)
> I have to say, Dr Frankenstein, that this idea fills me with dread.
> 
> I'm not saying it's impossible, but the resulting creature sounds like
> it's going to be special in several easily-buggy hard-to-maintain ways.
> 
> I think you already realize that shmem file pages (shared) live by
> different rules from anonymous pages (COWed): they're both swappable,
> but switching a group of pages from one to the other is going to be
> weird new territory.  (In fairness, my suggestion involves some
> weird new territory too, but considerably less scary to me.)

Umm...  Note that these guys are considerably simpler than shmem; _nothing_
will have them mapped anywhere until after that eviction and nothing will
modify their address_space in any way (no truncation, etc.).

And no, I'm not particulary happy about the picture - the sight of, ahem,
locking hierarcy rules in mm/filemap.c alone is a cause for dread.  It had
been a while since I'd done any serious RTFS on mm/*, so...

Anyway, it's obviously *not* -rc1 fodder at the moment.  So what I'm going
to do is to leave that one as it is in mainline, push the rest of mmap/mremap
stuff to Linus later today and get to VFS and audit queues.  After the -rc1,
OTOH...
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