From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id 415A66B02B4 for ; Tue, 7 Nov 2017 23:56:13 -0500 (EST) Received: by mail-pl0-f71.google.com with SMTP id f6so703611pln.9 for ; Tue, 07 Nov 2017 20:56:13 -0800 (PST) Received: from ozlabs.org (ozlabs.org. [103.22.144.67]) by mx.google.com with ESMTPS id u69si876459pgb.489.2017.11.07.20.56.11 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 07 Nov 2017 20:56:11 -0800 (PST) From: Michael Ellerman Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory In-Reply-To: <2ce0a91c-985c-aad8-abfa-e91bc088bb3e@linux.vnet.ibm.com> References: <20171105231850.5e313e46@roar.ozlabs.ibm.com> <871slcszfl.fsf@linux.vnet.ibm.com> <20171106174707.19f6c495@roar.ozlabs.ibm.com> <24b93038-76f7-33df-d02e-facb0ce61cd2@redhat.com> <20171106192524.12ea3187@roar.ozlabs.ibm.com> <546d4155-5b7c-6dba-b642-29c103e336bc@redhat.com> <20171107160705.059e0c2b@roar.ozlabs.ibm.com> <20171107111543.ep57evfxxbwwlhdh@node.shutemov.name> <20171107222228.0c8a50ff@roar.ozlabs.ibm.com> <20171107122825.posamr2dmzlzvs2p@node.shutemov.name> <20171108002448.6799462e@roar.ozlabs.ibm.com> <2ce0a91c-985c-aad8-abfa-e91bc088bb3e@linux.vnet.ibm.com> Date: Wed, 08 Nov 2017 15:56:06 +1100 Message-ID: <87y3nh2wt5.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" , Nicholas Piggin , "Kirill A. Shutemov" Cc: Florian Weimer , linux-arch@vger.kernel.org, Dave Hansen , Peter Zijlstra , Linus Torvalds , Ingo Molnar , Linux Kernel Mailing List , Andy Lutomirski , linux-mm , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Thomas Gleixner , "Kirill A. Shutemov" "Aneesh Kumar K.V" writes: >> >> If it is decided to keep these kind of heuristics, can we get just a >> small but reasonably precise description of each change to the >> interface and ways for using the new functionality, such that would be >> suitable for the man page? I couldn't fix powerpc because nothing >> matches and even Aneesh and you differ on some details (MAP_FIXED >> behaviour). > > > I would consider MAP_FIXED as my mistake. We never discussed this > explicitly and I kind of assumed it to behave the same way. ie, we > search in lower address space (128TB) if the hint addr is below 128TB. > > IIUC we agree on the below. > > 1) MAP_FIXED allow the addr to be used, even if hint addr is below 128TB > but hint_addr + len is > 128TB. So: mmap(0x7ffffffff000, 0x2000, ..., MAP_FIXED ...) = 0x7ffffffff000 > 2) For everything else we search in < 128TB space if hint addr is below > 128TB mmap((x < 128T), 0x1000, ...) = (y < 128T) ... mmap(0x7ffffffff000, 0x1000, ...) = 0x7ffffffff000 mmap(0x800000000000, 0x1000, ...) = 0x800000000000 ... mmap((x >= 128T), 0x1000, ...) = (y >= 128T) > 3) We don't switch to large address space if hint_addr + len > 128TB. > The decision to switch to large address space is primarily based on hint > addr But does the mmap succeed in that case or not? ie: mmap(0x7ffffffff000, 0x2000, ...) = ? cheers -- 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