From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 21 Dec 2004 10:36:28 +0100 From: Andi Kleen Subject: Re: [RFC][PATCH 0/10] alternate 4-level page tables patches Message-ID: <20041221093628.GA6231@wotan.suse.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Hugh Dickins , Nick Piggin , Andi Kleen , Linux Memory Management , Andrew Morton List-ID: On Mon, Dec 20, 2004 at 07:56:36PM -0800, Linus Torvalds wrote: > > > On Mon, 20 Dec 2004, Linus Torvalds wrote: > > > > (It may be _possible_ to avoid the warnings by just making "pud_t" and > > "pmd_t" be the same type for such architectures, and just allowing > > _mixing_ of three-level and four-level accesses. I have to say that I > > consider that pretty borderline programming practice though). > > Actually, I notice that this is exactly what you did, sorry for not being > more careful about reading your defines. > > Thinking some more about it, I don't much like the "mixing" of 3-level and > 4-level things, but since the only downside is a lack of type-safety for > the 4-level case (ie you can get it wrong without getting any warning), > and since that type safety _does_ exist in the case where the four levels > are actually used, I think it's ok. Sorry, but I don't. > > It would be bad if the architecture that supported 4level page tables was > really rare and broken (so that mistakes would happen and not get noticed > for a while), but I suspect x86-64 by now is probably the second- or > third-most used architecture, so it's not like the lack of type safety on > other architectures where it doesn't matter would be a huge maintenance > problem. Sorry, but I think that's a very bad approach. If the i386 users don't get warnings I will need to spend a lot of time just patching behind them. While x86-64 is getting more and more popular most hacking still happens on i386. Please use a type safe approach that causes warnings and errors on i386 too. Otherwise it'll cause me much additional work longer term. Having the small advantage of a perhaps slightly easier migration for long term maintenance hazzle is a bad tradeoff IMHO. Also is the flag day really that bad? I already did near all the work IMHO (with the help of some architecture maintainers, thanks guys!) and the patches are really not *that* bad. Linus can you please at least take a second look at them before going with the non typesafe hack? Thanks, -Andi -- 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: aart@kvack.org