From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16C3BC04AA7 for ; Mon, 13 May 2019 19:15:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E12A5208C3 for ; Mon, 13 May 2019 19:15:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="NkJr9A6B" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729277AbfEMTPH (ORCPT ); Mon, 13 May 2019 15:15:07 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:37403 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729234AbfEMTPH (ORCPT ); Mon, 13 May 2019 15:15:07 -0400 Received: by mail-wm1-f66.google.com with SMTP id 7so441909wmo.2 for ; Mon, 13 May 2019 12:15:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:mime-version:content-disposition :user-agent; bh=PxThcXQElVI91fi7m64BrSH6eJF9eKRKuatu0rpXtiA=; b=NkJr9A6BNcXWpAQOkQGs5yi+BsqG4+jd1NwObELbXnetvTywfesP6FGR7fRX8oN4p0 F3gdptrv3yvWC9QgGz1NKXwpOEtuSMgPrF3FGNoyk6ASphdkzr5BKUUkZlKSNjWjhed2 nXRSQTiaSCyXZfHbRh7s4dc49zOsKrV0xNgQckeadFVC1WOP3oxET0zuaRWiN9HQlDRU +K/00YfO8CFeQ3NSmR1AP5INJ5YoYe8TLzfVK27rKvoQ4JcQ4pRuHXofZulH48CH5UvG u7ptofrbRq4zsC5i2VomP9XnWae3DDw1bZ+cEAqXLCtbYfh+iLmUhaSAp5gOwMYhaopO AyiQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition:user-agent; bh=PxThcXQElVI91fi7m64BrSH6eJF9eKRKuatu0rpXtiA=; b=Mth/lmX6VfKgaQUfSNRMvOzA/eGi6u1kABsIuzuXBoC/kJ6SUxoatiCYW5KkhYu3ni thsnxyxWwwVHA1TcFKWx8Sd2sey1MHqRzPwzDM0TODxz0nwiMreBrfuoCQDtQVH+HZSm o29FO6U6hQ6SRdEXORIpnJuqeWaYDKxe7IS7JEwHyKqgh2woAKZEnSc9S7HfscXCI7+o TKjks8hYs0AMeRReGL05/SavulklZp+ySWasZNixtUd2eB1qKXXf87Ezgvy0ukc/fiXP IMAl3DB8SZcQXU6A5qImsBzmA0/yHSrqywSlPF08oZUfwAwb3GYUMdEQL6MFyfHh39ck bxqQ== X-Gm-Message-State: APjAAAUkpbGcVv1oQt9T+n+HHW5bdS76CvKe5hJPLNbjQjd8K3a2pYE/ pJNlHi/Pa10BKsc4ADlSFXsXFkI= X-Google-Smtp-Source: APXvYqx4dIMN7CzriD9A4cTd7ina5RxiwjqvDU3bJ3Zr0XndeMDk3N+t9f84fF/FJMhCUYWcYz6yFQ== X-Received: by 2002:a1c:1ad6:: with SMTP id a205mr4355150wma.80.1557774905276; Mon, 13 May 2019 12:15:05 -0700 (PDT) Received: from avx2 ([46.53.253.112]) by smtp.gmail.com with ESMTPSA id 4sm16264208wrf.61.2019.05.13.12.15.03 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 May 2019 12:15:04 -0700 (PDT) Date: Mon, 13 May 2019 22:15:02 +0300 From: Alexey Dobriyan To: akpm@linux-foundation.org Cc: segoon@openwall.com, linux-kernel@vger.kernel.org Subject: [PATCH] tweak LIST_POISON2 for better code generation on x86_64 Message-ID: <20190513191502.GA8492@avx2> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org list_del() poisoning can generate 2 64-bit immediate loads but it also can generate one 64-bit immediate load and an addition: 48 b8 00 01 00 00 00 00 ad de movabs rax,0xdead000000000100 48 89 47 58 mov QWORD PTR [rdi+0x58],rax 48 05 00 01 00 00 <=====> add rax,0x100 48 89 47 60 mov QWORD PTR [rdi+0x60],rax However on x86_64 not all constants are equal: those within [-128, 127] range can be added with shorter "add r64, imm32" instruction: 48 b8 00 01 00 00 00 00 ad de movabs rax,0xdead000000000100 48 89 47 58 mov QWORD PTR [rdi+0x58],rax 48 83 c0 22 <======> add rax,0x22 48 89 47 60 mov QWORD PTR [rdi+0x60],rax Patch saves 2 bytes per some LIST_POISON2 usage. (Slightly disappointing) space savings on F29 x86_64 config: add/remove: 0/0 grow/shrink: 0/2164 up/down: 0/-5184 (-5184) Function old new delta zstd_get_workspace 548 546 -2 ... mlx4_delete_all_resources_for_slave 4826 4804 -22 Total: Before=83304131, After=83298947, chg -0.01% New constants are: 0xdead000000000100 0xdead000000000122 Note: LIST_POISON1 can't be changed to ...11 because something in page allocator requires low bit unset. Signed-off-by: Alexey Dobriyan --- include/linux/poison.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -21,7 +21,7 @@ * non-initialized list entries. */ #define LIST_POISON1 ((void *) 0x100 + POISON_POINTER_DELTA) -#define LIST_POISON2 ((void *) 0x200 + POISON_POINTER_DELTA) +#define LIST_POISON2 ((void *) 0x122 + POISON_POINTER_DELTA) /********** include/linux/timer.h **********/ /*