From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 3 Oct 2007 08:21:51 -0700 (PDT) From: Linus Torvalds Subject: Re: remove zero_page (was Re: -mm merge plans for 2.6.24) In-Reply-To: <200710030345.10026.nickpiggin@yahoo.com.au> Message-ID: References: <20071001142222.fcaa8d57.akpm@linux-foundation.org> <200710030345.10026.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org