Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756232Ab2JVVjm (ORCPT ); Mon, 22 Oct 2012 17:39:42 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:42069 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754337Ab2JVVjl (ORCPT ); Mon, 22 Oct 2012 17:39:41 -0400 Date: Mon, 22 Oct 2012 14:39:40 -0700 From: Andrew Morton To: Andi Kleen Cc: Michael Kerrisk , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andi Kleen , Hillf Danton Subject: Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Message-Id: <20121022143940.6bf8103f.akpm@linux-foundation.org> In-Reply-To: <20121022132733.GQ16230@one.firstfloor.org> References: <1350665289-7288-1-git-send-email-andi@firstfloor.org> <20121022132733.GQ16230@one.firstfloor.org> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 36 On Mon, 22 Oct 2012 15:27:33 +0200 Andi Kleen wrote: > BTW seriously MAP_UNINITIALIZED? Who came up with that? > MAP_COMPLETELY_INSECURE or MAP_INSANE would have been more appropiate. heh. It's a NOMMU-only thing. config MMAP_ALLOW_UNINITIALIZED bool "Allow mmapped anonymous memory to be uninitialized" depends on EXPERT && !MMU default n help Normally, and according to the Linux spec, anonymous memory obtained from mmap() has it's contents cleared before it is passed to userspace. Enabling this config option allows you to request that mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus providing a huge performance boost. If this option is not enabled, then the flag will be ignored. This is taken advantage of by uClibc's malloc(), and also by ELF-FDPIC binfmt's brk and stack allocator. Because of the obvious security issues, this option should only be enabled on embedded devices where you control what is run in userspace. Since that isn't generally a problem on no-MMU systems, it is normally safe to say Y here. See Documentation/nommu-mmap.txt for more information. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/