From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f197.google.com (mail-ua0-f197.google.com [209.85.217.197]) by kanga.kvack.org (Postfix) with ESMTP id 4DC1C6B0038 for ; Fri, 17 Feb 2017 15:12:53 -0500 (EST) Received: by mail-ua0-f197.google.com with SMTP id x12so31232396uax.6 for ; Fri, 17 Feb 2017 12:12:53 -0800 (PST) Received: from mail-ua0-x230.google.com (mail-ua0-x230.google.com. [2607:f8b0:400c:c08::230]) by mx.google.com with ESMTPS id j17si1134172uaf.188.2017.02.17.12.12.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Feb 2017 12:12:52 -0800 (PST) Received: by mail-ua0-x230.google.com with SMTP id k3so1374849uak.2 for ; Fri, 17 Feb 2017 12:12:52 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <20170217141328.164563-1-kirill.shutemov@linux.intel.com> <20170217141328.164563-34-kirill.shutemov@linux.intel.com> From: Andy Lutomirski Date: Fri, 17 Feb 2017 12:12:31 -0800 Message-ID: Subject: Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: "Kirill A. Shutemov" , Andrew Morton , the arch/x86 maintainers , Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" , Andi Kleen , Dave Hansen , "linux-arch@vger.kernel.org" , linux-mm , Linux Kernel Mailing List , Catalin Marinas , Linux API On Fri, Feb 17, 2017 at 12:02 PM, Linus Torvalds wrote: > On Fri, Feb 17, 2017 at 6:13 AM, Kirill A. Shutemov > wrote: >> This patch introduces two new prctl(2) handles to manage maximum virtual >> address available to userspace to map. > > So this is my least favorite patch of the whole series, for a couple of reasons: > > (a) adding new code, and mixing it with the mindless TASK_SIZE -> > get_max_addr() conversion. > > (b) what's the point of that whole TASK_SIZE vs get_max_addr() thing? > When use one, when the other? > > so I think this patch needs a lot more thought and/or explanation. > > Honestly, (a) is a no-brainer, and can be fixed by just splitting the > patch up. But I think (b) is more fundamental. > > In particular, I think that get_max_addr() thing is badly defined. > When should you use TASK_SIZE, when should you use TASK_SIZE_MAX, and > when should you use get_max_addr()? I don't find that clear at all, > and I think that needs to be a whole lot more explicit and documented. > > I also get he feeling that the whole thing is unnecessary. I'm > wondering if we should just instead say that the whole 47 vs 56-bit > virtual address is _purely_ about "get_unmapped_area()", and nothing > else. > > IOW, I'm wondering if we can't just say that > > - if the processor and kernel support 56-bit user address space, then > you can *always* use the whole space > > - but by default, get_unmapped_area() will only return mappings that > fit in the 47 bit address space. > > So if you use MAP_FIXED and give an address in the high range, it will > just always work, and the MM will always consider the task size to be > the full address space. At the very least, I'd want to see MAP_FIXED_BUT_DONT_BLOODY_UNMAP_ANYTHING. I *hate* the current interface. > > But for the common case where a process does no use MAP_FIXED, the > kernel will never give a high address by default, and you have to do > the process control thing to say "I want those high addresses". > > Hmm? How about MAP_LIMIT where the address passed in is interpreted as an upper bound instead of a fixed address? --Andy -- 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