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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 2451CC433B4 for ; Wed, 7 Apr 2021 02:50:39 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BB0D66124B for ; Wed, 7 Apr 2021 02:50:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB0D66124B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5DE156B007E; Tue, 6 Apr 2021 22:50:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5B4846B0081; Tue, 6 Apr 2021 22:50:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4A3146B0082; Tue, 6 Apr 2021 22:50:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0018.hostedemail.com [216.40.44.18]) by kanga.kvack.org (Postfix) with ESMTP id 2E92C6B007E for ; Tue, 6 Apr 2021 22:50:38 -0400 (EDT) Received: from smtpin34.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E1CAA1803EF28 for ; Wed, 7 Apr 2021 02:50:37 +0000 (UTC) X-FDA: 78004042914.34.5A20CA4 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf14.hostedemail.com (Postfix) with ESMTP id 39D66C0001F7 for ; Wed, 7 Apr 2021 02:50:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=dV1f1V+Do2hXUWRE6FICi+uU6gH6OPiZlIka5qV9wTc=; b=EveHe1q6JfT5AQikfGrlIYCz7m BZNqbrVTzWqjZ8zyTxsRk+hByPGSy9K0REt+n7eXSCiDrUAO/fJasjEVrC0Yh1jh/OjDLE3WTj9Sv XIWscA0NNiWr1s7BxhXWBibcNXmR9P6y8MR0MaSivH/T7cKmLeJb0J3S1Dic93w9DUQDRgr9kk8wP 9EMOwPGAtiyrmYuCXsmTL6b4NHLWaK2WoHm+/x0SJcwjNfiYGEgVe/bbssgOBrjKSWOtJlK0A47Nn d4WPDk9idARg4jZ2lKEuZxwTJM3groRjYlGdtjFuZQREdgnsI2MRBhCh7DjUgvIRFXbq32Qtz0n/1 ApQBq/5A==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lTyGc-00Dmua-LB; Wed, 07 Apr 2021 02:50:11 +0000 Date: Wed, 7 Apr 2021 03:50:06 +0100 From: Matthew Wilcox To: Michel Lespinasse Cc: Linux-MM , Laurent Dufour , Peter Zijlstra , Michal Hocko , Rik van Riel , Paul McKenney , Andrew Morton , Suren Baghdasaryan , Joel Fernandes , Rom Lemarchand , Linux-Kernel Subject: Re: [RFC PATCH 34/37] mm: rcu safe vma freeing only for multithreaded user space Message-ID: <20210407025006.GB2531743@casper.infradead.org> References: <20210407014502.24091-1-michel@lespinasse.org> <20210407014502.24091-35-michel@lespinasse.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210407014502.24091-35-michel@lespinasse.org> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 39D66C0001F7 X-Stat-Signature: jpsk8x16fhahtnpkyodkdyixxtxbnyr1 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617763833-7505 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 Tue, Apr 06, 2021 at 06:44:59PM -0700, Michel Lespinasse wrote: > Performance tuning: as single threaded userspace does not use > speculative page faults, it does not require rcu safe vma freeing. > Turn this off to avoid the related (small) extra overheads. > > For multi threaded userspace, we often see a performance benefit from > the rcu safe vma freeing - even in tests that do not have any frequent > concurrent page faults ! This is because rcu safe vma freeing prevents > recently released vmas from being immediately reused in a new thread. Why does that provide a performance benefit? Recently released VMAs are cache-hot, and NUMA-local. I'd expect the RCU delay to be performance-negative.