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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A54CC4332F for ; Mon, 17 Oct 2022 22:33:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229889AbiJQWdO (ORCPT ); Mon, 17 Oct 2022 18:33:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229597AbiJQWdN (ORCPT ); Mon, 17 Oct 2022 18:33:13 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3C1BF748C2 for ; Mon, 17 Oct 2022 15:33:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 3415AB81B67 for ; Mon, 17 Oct 2022 22:33:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E7D49C433D7; Mon, 17 Oct 2022 22:33:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1666045989; bh=lM5uPW7I10WHZ5h+A7/uPn2bqwqIUxbF/xMqmHxLbvA=; h=Date:To:From:Subject:From; b=okXMEl8GIPrpcTwyhCw0jYAv1+8lbyT3T0qjyJLnzNIs///SGMM91q2ZNYlTHpRK8 i/n1XKiKggUhOdaCWSzThkIgQ+FuSrTgAOgs11sJqF0dlDgLsBV09wEVbIzVvmIdnv P7G71wVAONAu6jQQ0T9pKafWnedgEbbxh6CR0IUo= Date: Mon, 17 Oct 2022 15:33:08 -0700 To: mm-commits@vger.kernel.org, ubizjak@gmail.com, akpm@linux-foundation.org From: Andrew Morton Subject: + llist-avoid-extra-memory-read-in-llist_add_batch.patch added to mm-nonmm-unstable branch Message-Id: <20221017223308.E7D49C433D7@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: llist: avoid extra memory read in llist_add_batch has been added to the -mm mm-nonmm-unstable branch. Its filename is llist-avoid-extra-memory-read-in-llist_add_batch.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/llist-avoid-extra-memory-read-in-llist_add_batch.patch This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Uros Bizjak Subject: llist: avoid extra memory read in llist_add_batch Date: Mon, 17 Oct 2022 16:52:26 +0200 try_cmpxchg implicitly assigns old head->first value to "first" when cmpxchg fails. There is no need to re-read the value in the loop. Link: https://lkml.kernel.org/r/20221017145226.4044-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Signed-off-by: Andrew Morton --- lib/llist.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/lib/llist.c~llist-avoid-extra-memory-read-in-llist_add_batch +++ a/lib/llist.c @@ -26,10 +26,10 @@ bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, struct llist_head *head) { - struct llist_node *first; + struct llist_node *first = READ_ONCE(head->first); do { - new_last->next = first = READ_ONCE(head->first); + new_last->next = first; } while (!try_cmpxchg(&head->first, &first, new_first)); return !first; _ Patches currently in -mm which might be from ubizjak@gmail.com are llist-avoid-extra-memory-read-in-llist_add_batch.patch