From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx166.postini.com [74.125.245.166]) by kanga.kvack.org (Postfix) with SMTP id 0F3F36B005A for ; Mon, 22 Oct 2012 12:06:46 -0400 (EDT) Date: Mon, 22 Oct 2012 08:36:33 -0700 From: Andi Kleen Subject: Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Message-ID: <20121022153633.GK2095@tassilo.jf.intel.com> References: <1350665289-7288-1-git-send-email-andi@firstfloor.org> <20121022132733.GQ16230@one.firstfloor.org> <20121022133534.GR16230@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: "Michael Kerrisk (man-pages)" Cc: Andi Kleen , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hillf Danton > Not sure of your notation there. I assume 31..27 means 5 bits (32 > through to 28 inclusive, 27 excluded). That gives you just 2^31 == [27...31] You're right it's only 5 bits, so just 2GB. Thinking about it more PowerPC has a 16GB page, so we probably need to move this to prot. However I'm not sure if any architectures use let's say the high 8 bits of prot. > > But there seems an obvious solution here: given your value in those > bits (call it 'n'), the why not apply a multiplier. I mean, certainly > you never want a value <= 12 for n, and I suspect that the reasonable > minimum could be much larger (e.g., 2^16). Call that minimum M. Then > you could interpret the value in your bits as meaning a page size of > > (2^n) * M I considered that, but it would seem ugly and does not add that many bits. > > > So this will use up all remaining flag bits now. > > On the other hand, that seems really bad. It looks like that kills the > ability to further extend the mmap() API with new flags in the future. > It doesn't sound like we should be doing that. You can always add flags to PROT or add a mmap3(). Has been done before. Or just don't do any new MAP_SECURITY_HOLEs -Andi -- ak@linux.intel.com -- Speaking for myself only -- 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