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 3116CC38159 for ; Thu, 19 Jan 2023 00:28:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 43EB36B0072; Wed, 18 Jan 2023 19:28:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3EEBF6B0073; Wed, 18 Jan 2023 19:28:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2DE316B0074; Wed, 18 Jan 2023 19:28:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 19EFD6B0072 for ; Wed, 18 Jan 2023 19:28:53 -0500 (EST) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id CA2DC120167 for ; Thu, 19 Jan 2023 00:28:52 +0000 (UTC) X-FDA: 80369663304.06.ABA9AE2 Received: from r3-11.sinamail.sina.com.cn (r3-11.sinamail.sina.com.cn [202.108.3.11]) by imf05.hostedemail.com (Postfix) with ESMTP id 9757C100009 for ; Thu, 19 Jan 2023 00:28:49 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.11 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674088131; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6O2XeLietrQbUiCeOum270fZylYgq9PPe8MS047J5RY=; b=glCKBHda55y7BosUhPBSA5K9Wo8+3nValue1OZZfeir7v2f7CrqulpG0WOIwMUvHFouw14 rz/7A4j3M9UFmt+R5lKhM7XoUB4IoOyeulafM00WBfZR4Ku8qpsOVIYpqjnTQZVI5O0ejA PbX4nFS+6N3VM8/VLnFzC1L7llyGOLQ= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.11 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674088131; a=rsa-sha256; cv=none; b=Bx2yBf5KOUNsUi5q0bzVz7elmEkEtI01LjbtACsY12WbCtp1FCNCGn1EwL6XxIWcqf5Xl0 68oACUBcgTRfiR4sJQBwtSlyEUe+UIWtOUYbaRZ/m+lfYC+9VUKN6Uy09GfwRSmCgwjCgC Z2+Ewk0hf0RRxsmAmLw1h9ejFJ2vrFE= Received: from unknown (HELO localhost.localdomain)([114.249.61.130]) by sina.com (172.16.97.27) with ESMTP id 63C88E53000317D9; Thu, 19 Jan 2023 08:27:01 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 23227749289220 From: Hillf Danton To: Matthew Wilcox Cc: Suren Baghdasaryan , vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, peterz@infradead.org, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock Date: Thu, 19 Jan 2023 08:28:33 +0800 Message-Id: <20230119002833.3191-1-hdanton@sina.com> In-Reply-To: References: <20230109205336.3665937-42-surenb@google.com> <20230116140649.2012-1-hdanton@sina.com> <20230117031632.2321-1-hdanton@sina.com> <20230117083355.2374-1-hdanton@sina.com> <20230118062639.2839-1-hdanton@sina.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9757C100009 X-Rspam-User: X-Stat-Signature: tiqdckw36hq44dmq6m7wjtj6icz7fg37 X-HE-Tag: 1674088129-21337 X-HE-Meta: U2FsdGVkX19Rmtrwm+9WYh1QfvJfxZhVNG81mQSyd7zQX9p1mAs7FknsLNo+gj6DnciGk6zBNrWB6y1Cur4fsFUi6AEgxKPmcXtE5b6j87CytR/PxEOIitzXFJivdrXBwdor+1m+DW/SHBAkElB0rIb6mhD18dA59Wh9eoR6/PEoiQkJvqmZ7TI7/pUiWeZtsmwZOgHvZOFAywauSbZQ2IlgodB4IKukp0o7kku6ZLCqSWoCU732NIMN169/LctAeA26QIf+2oVxLxsS8jZ+DFc5FAj2lq01QoYF8FutBKQbTLoAuVTFnInAmUjinWQEq7J1yL2NtxzrQMyvE9NiemTj1KSc9HprACW8ote9TDz3eeg6/Lt4F/rpHYfNn4Iw+lyrVq7Jw+1VYWcxrJDBC0A3T/nXKbYDoG5N2M7g3gLCJ4cfkuu8DNaAOCvtiPmyUriwFFtSzfXIn0GxBRacV+XHFsnOgv+4r1A3Xy1f3tvpWlhaARwf+k6zsNycPmbfvV1lqD1rSpezsPWmuEG2Qy9PnsNWLpaaEEKAPumqH0dzIHTuNOBELgk/RimdwkEvGez9kZ9qrqAy76+mfMcFao/aLBeEFcSm/0k/SZsM2DSQlkGqdWDAbh67w+m7olCinxI6eh++QBOR2PXL+KqLInj1AR7dZnqIcXoy+TfJf7iRonY1z5hqJUVxp+7Pc2xYeNBxf6F2nltRamoWG0PwkSh/pEE6wCYlx+6vaUojrRO3lZo+uboc73KfcqN4X0qAmoCt/3deOqnPlmdZI1kXcHQEB1mbwCWZ+R+qfzaivF7zT8YjI/Lnr0TVKLJEU7hOhzLxFjVD+bg7kWmR4qTNHA== 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, 18 Jan 2023 18:35:13 +0000 Matthew Wilcox wrote: > On Wed, Jan 18, 2023 at 02:26:39PM +0800, Hillf Danton wrote: > > On Tue, Jan 17, 2023 at 10:27 AM Matthew Wilcox wrote: > > > > > > The cpu_relax() is exactly the wrong thing to do here. See this thread: > > > https://lore.kernel.org/linux-fsdevel/20230113184447.1707316-1-mjguzik@gmail.com/ > > > > If you are right, feel free to go and remove every cpu_relax() under the > > kernel/locking directory. > > I see you didn't read the whole thread where Linus points out that a > cmpxchg() loop is fundamentally different from a spinlock. Hm... I try hard to sidestep the dilemma - I prefer to follow the voice under the locking directory even given his voice. And in this case, trylock, the failure of acquiring the lock only means fine because it is fine for whoever to become the lock owner.