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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 D127AC433E1 for ; Thu, 18 Jun 2020 17:32:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 97B20208C3 for ; Thu, 18 Jun 2020 17:32:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="UlADRr7W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97B20208C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3039C8D004A; Thu, 18 Jun 2020 13:32:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 28D1B8D0018; Thu, 18 Jun 2020 13:32:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 17CCB8D004A; Thu, 18 Jun 2020 13:32:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0180.hostedemail.com [216.40.44.180]) by kanga.kvack.org (Postfix) with ESMTP id F145A8D0018 for ; Thu, 18 Jun 2020 13:32:08 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 92D19824805A for ; Thu, 18 Jun 2020 17:32:08 +0000 (UTC) X-FDA: 76943025936.21.swing45_43037ac26e12 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 63BAC180442CD for ; Thu, 18 Jun 2020 17:32:08 +0000 (UTC) X-HE-Tag: swing45_43037ac26e12 X-Filterd-Recvd-Size: 3872 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Thu, 18 Jun 2020 17:32:07 +0000 (UTC) Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D0AFA208B8; Thu, 18 Jun 2020 17:32:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592501526; bh=yTsrBl2tE3fnFEIPv5CpTnTJlef/tgV4kZQ5U8GHJPk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=UlADRr7WPtcKFU60fOr0nPBXKkKCmTiJXKtK1awwyyMozYrumEaYzjk4gKRCbAKZx dKEY7iMvjfLaSg1faXq+gXFitw+PT6LJj/ZiTrrN32GzQMD1MzSiunYq7D2hxeMWp7 ssY1umEG+TBGUQMrb02kMW5n51sLBp+H9edLded8= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id AEC9E35229B4; Thu, 18 Jun 2020 10:32:06 -0700 (PDT) Date: Thu, 18 Jun 2020 10:32:06 -0700 From: "Paul E. McKenney" To: Uladzislau Rezki Cc: LKML , linux-mm@kvack.org, Andrew Morton , "Theodore Y . Ts'o" , Matthew Wilcox , Joel Fernandes , RCU , Oleksiy Avramchenko Subject: Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs Message-ID: <20200618173206.GS2723@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200525214800.93072-1-urezki@gmail.com> <20200525214800.93072-10-urezki@gmail.com> <20200617234609.GA10087@paulmck-ThinkPad-P72> <20200618172504.GA14613@pc636> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200618172504.GA14613@pc636> User-Agent: Mutt/1.9.4 (2018-02-28) X-Rspamd-Queue-Id: 63BAC180442CD X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jun 18, 2020 at 07:25:04PM +0200, Uladzislau Rezki wrote: > > > + // Handle two first channels. > > > + for (i = 0; i < FREE_N_CHANNELS; i++) { > > > + for (; bkvhead[i]; bkvhead[i] = bnext) { > > > + bnext = bkvhead[i]->next; > > > + debug_rcu_bhead_unqueue(bkvhead[i]); > > > + > > > + rcu_lock_acquire(&rcu_callback_map); > > > + if (i == 0) { // kmalloc() / kfree(). > > > + trace_rcu_invoke_kfree_bulk_callback( > > > + rcu_state.name, bkvhead[i]->nr_records, > > > + bkvhead[i]->records); > > > + > > > + kfree_bulk(bkvhead[i]->nr_records, > > > + bkvhead[i]->records); > > > + } else { // vmalloc() / vfree(). > > > + for (j = 0; j < bkvhead[i]->nr_records; j++) { > > > + trace_rcu_invoke_kfree_callback( > > > + rcu_state.name, > > > + bkvhead[i]->records[j], 0); > > > + > > > + vfree(bkvhead[i]->records[j]); > > > + } > > > + } > > > + rcu_lock_release(&rcu_callback_map); > > > > Not an emergency, but did you look into replacing this "if" statement > > with an array of pointers to functions implementing the legs of the > > "if" statement? If nothing else, this would greatly reduced indentation. > > > > > > I am taking this as is, but if you have not already done so, could you > > please look into this for a follow-up patch? > > > I do not think it makes sense, because it would require to check each > pointer in the array, what can lead to many branching, i.e. "if-else" > instructions. Mightn't the compiler simply unroll the outer loop? Then the first unrolled iteration of that loop would contain the then-clause and the second unrolled iteration would contain the else-clause. At that point, there would be no checking, just direct calls. Or am I missing something? > Paul, thank you to take it in! Thank you for persisting! Thanx, Paul