linux-kernel - Re: remove zero_page (was Re: -mm merge plans for 2.6.24)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.LFD.0.999.0710030813090.3579@woody.linux-foundation.org>
Date:	Wed, 3 Oct 2007 08:21:51 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: remove zero_page (was Re: -mm merge plans for 2.6.24)

On Wed, 3 Oct 2007, Nick Piggin wrote:
> 
> I don't know if Linus actually disliked the patch itself, or disliked
> my (maybe confusingly worded) rationale?

Yes. I'd happily accept the patch, but I'd want it clarified and made 
obvious what the problem was - and it wasn't the zero page itself, it was 
a regression in the VM that made it less palatable.

I also thought that there were potentially better solutions, namely to 
simply avoid the VM regression, but I also acknowledge that they may not 
be worth it - I just want them to be on the table.

In short: the real cost of the zero page was the reference counting on the 
page that we do these days. For example, I really do believe that the 
problem could fairly easily be fixed by simply not considering zero_page
to be a "vm_normal_page()". We already *do* have support for pages not 
getting ref-counted (since we need it for other things), and I think that 
zero_page very naturally falls into exactly that situation.

So in many ways, I would think that turning zero-page into a nonrefcounted 
page (the same way we really do have to do for other things anyway) would 
be the much more *direct* solution, and in many ways the obvious one.

HOWEVER - if people think that it's easier to remove zero_page, and want 
to do it for other reasons, *AND* can hopefully even back up the claim 
that it never matters with numbers (ie that the extra pagefaults just make 
the whole zero-page thing pointless), then I'd certainly accept the patch. 

I'd just want the patch *description* to then also be correct, and blame 
the right situation, instead of blaming zero-page itself.

		Linus
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/