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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8D4FC00140 for ; Thu, 18 Aug 2022 10:19:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 541786B0073; Thu, 18 Aug 2022 06:19:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4F1146B0074; Thu, 18 Aug 2022 06:19:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 407658D0001; Thu, 18 Aug 2022 06:19:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 328FF6B0073 for ; Thu, 18 Aug 2022 06:19:41 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id F31511A09DA for ; Thu, 18 Aug 2022 10:19:40 +0000 (UTC) X-FDA: 79812316920.18.1F53062 Received: from gentwo.de (gentwo.de [161.97.139.209]) by imf07.hostedemail.com (Postfix) with ESMTP id CAB784137E for ; Thu, 18 Aug 2022 09:50:52 +0000 (UTC) Received: by gentwo.de (Postfix, from userid 1001) id E8493B002B2; Thu, 18 Aug 2022 11:42:00 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gentwo.de; s=default; t=1660815720; bh=zhSk3gUIK+mDi9XiV4NGeRbdkgpqWbv2DEwABjWuxDQ=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=MOziH+YXigIkZ5JoZLci/yn9Gsmc5kVya7ebi8NlUx2Mk+PUFJzY6Pd9zDtq2u4ge HL5vzZwPLJJbtVtfiJHfbNJ2ZMX2wiIYJHr0EsvZMMIpl8eOJI52sU/DEScOsn6PSl X2ZGEaOwB7usppzCAszgv2dEF8pieXdlntgSGnVUL/OecgcrnoeM0akruQbsrtdFPC Qx6OWJtinEgPo28VEmfu3aB8KF4jfe31R3f9Ty00MssEDM4iYDbEhBgkvmxE0yaHcy kMFwttrnRmayXK04n4Seo5h32BPHNRDkP+M5p37qrByLFNc3SKkqLM0U3JXtFH+Gba u5pkcG1JMDpZw== Received: from localhost (localhost [127.0.0.1]) by gentwo.de (Postfix) with ESMTP id E48CDB00210; Thu, 18 Aug 2022 11:42:00 +0200 (CEST) Date: Thu, 18 Aug 2022 11:42:00 +0200 (CEST) From: Christoph Lameter To: Sebastian Andrzej Siewior cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Linus Torvalds , Matthew Wilcox , Andrew Morton , David Rientjes , Joonsoo Kim , Pekka Enberg , Vlastimil Babka , linux-mm@kvack.org Subject: Re: [PATCH 1/9] slub: Make PREEMPT_RT support less convoluted In-Reply-To: <20220817162703.728679-2-bigeasy@linutronix.de> Message-ID: References: <20220817162703.728679-1-bigeasy@linutronix.de> <20220817162703.728679-2-bigeasy@linutronix.de> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660816254; a=rsa-sha256; cv=none; b=aYBhzQwiXdKGyoR2r3uwa4ey3tpdyJWoZIrLiwT2iezmybRmxA1NxOrhSLxE/rHkahXUch X/qix/tljK3qI5FDL+2Ee3S/zYrDJ8XV6h9vh0ZnedxUfy0qrccEt///K42JNBy7B7+iBu WntbflRTdhp43cfsBwkBBF+yb2ozaVI= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=none ("invalid DKIM record") header.d=gentwo.de header.s=default header.b=MOziH+YX; dmarc=pass (policy=none) header.from=gentwo.de; spf=pass (imf07.hostedemail.com: domain of cl@gentwo.de designates 161.97.139.209 as permitted sender) smtp.mailfrom=cl@gentwo.de ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660816254; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=sXcbbJ6oTTf0VpQ4qRfY0DnpBrem73eDysEBswlNX18=; b=gdSGUD5WAm+5QUeD2migu6Wg0iKDd6J9gFqbp5KeTzwkpyossA9NqktgpBbdmj3z8apqvZ jswkKcxrO5J8HkltcDLU/ZMMIUdD6ge5RhmHBwID1Az2gwLRWyE/Yv2YjLzGHmMgdNCaLU 2ZoFdk3++SW4rWpDp8sHm8nRnT57Zos= X-Stat-Signature: kjwajq3ztapnxmwmh7fa1smdddtne8m4 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: CAB784137E X-Rspam-User: Authentication-Results: imf07.hostedemail.com; dkim=none ("invalid DKIM record") header.d=gentwo.de header.s=default header.b=MOziH+YX; dmarc=pass (policy=none) header.from=gentwo.de; spf=pass (imf07.hostedemail.com: domain of cl@gentwo.de designates 161.97.139.209 as permitted sender) smtp.mailfrom=cl@gentwo.de X-HE-Tag: 1660816252-749628 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 Wed, 17 Aug 2022, Sebastian Andrzej Siewior wrote: > + * On PREEMPT_RT, the local lock neither disables interrupts nor preemption > + * which means the lockless fastpath cannot be used as it might interfere with > + * an in-progress slow path operations. In this case the local lock is always > + * taken but it still utilizes the freelist for the common operations. The slub fastpath does not interfere with slow path operations and the fastpath does not require disabling preemption or interrupts if the processor supports local rmv operations. So you should be able to use the fastpath on PREEMPT_RT. If the fastpath is not possible then you need to disable preemption and eventually take locks etc and then things may get a bit more complicated.