From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f53.google.com (mail-pa0-f53.google.com [209.85.220.53]) by kanga.kvack.org (Postfix) with ESMTP id E0A216B0005 for ; Thu, 24 Mar 2016 18:36:40 -0400 (EDT) Received: by mail-pa0-f53.google.com with SMTP id td3so32419337pab.2 for ; Thu, 24 Mar 2016 15:36:40 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id r72si1388310pfb.235.2016.03.24.15.36.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Mar 2016 15:36:40 -0700 (PDT) Date: Thu, 24 Mar 2016 15:36:39 -0700 From: Andrew Morton Subject: Re: [PATCH 2/2] include/linux: apply __malloc attribute Message-Id: <20160324153639.bb996d7bf5a585dfb46740b7@linux-foundation.org> In-Reply-To: <1458776553-9033-2-git-send-email-linux@rasmusvillemoes.dk> References: <1458776553-9033-1-git-send-email-linux@rasmusvillemoes.dk> <1458776553-9033-2-git-send-email-linux@rasmusvillemoes.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rasmus Villemoes Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andi Kleen , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Thu, 24 Mar 2016 00:42:32 +0100 Rasmus Villemoes wrote: > Attach the malloc attribute to a few allocation functions. This helps > gcc generate better code by telling it that the return value doesn't > alias any existing pointers (which is even more valuable given the > pessimizations implied by -fno-strict-aliasing). > > A simple example of what this allows gcc to do can be seen by looking > at the last part of drm_atomic_helper_plane_reset: > > plane->state = kzalloc(sizeof(*plane->state), GFP_KERNEL); > > if (plane->state) { > plane->state->plane = plane; > plane->state->rotation = BIT(DRM_ROTATE_0); > } > > which compiles to > > e8 99 bf d6 ff callq ffffffff8116d540 > 48 85 c0 test %rax,%rax > 48 89 83 40 02 00 00 mov %rax,0x240(%rbx) > 74 11 je ffffffff814015c4 > 48 89 18 mov %rbx,(%rax) > 48 8b 83 40 02 00 00 mov 0x240(%rbx),%rax [*] > c7 40 40 01 00 00 00 movl $0x1,0x40(%rax) > > With this patch applied, the instruction at [*] is elided, since the > store to plane->state->plane is known to not alter the value of > plane->state. Shaves 6 bytes off my 1MB i386 defconfig vmlinux. Winner! -- 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