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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDAD4C433F5 for ; Fri, 15 Oct 2021 06:30:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E0084610E5 for ; Fri, 15 Oct 2021 06:30:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E0084610E5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 77DA76B006C; Fri, 15 Oct 2021 02:30:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 706316B0071; Fri, 15 Oct 2021 02:30:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5CEC1900002; Fri, 15 Oct 2021 02:30:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0106.hostedemail.com [216.40.44.106]) by kanga.kvack.org (Postfix) with ESMTP id 4A8A36B006C for ; Fri, 15 Oct 2021 02:30:09 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 05AB02BC00 for ; Fri, 15 Oct 2021 06:30:09 +0000 (UTC) X-FDA: 78697696938.06.0680D78 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf19.hostedemail.com (Postfix) with ESMTP id DCB9AB00009D for ; Fri, 15 Oct 2021 06:30:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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=Nv5FQ/6vTqDP+uvH/XRZgii5X0jrEJS0CQSXWJp5LYY=; b=AgLYGCmRq2PJF2LjCKSd3i9+8e dHwI13PRvpN84mnLWiuxm2DChcEhVcL2j5+G1MpSJir3s0No/Qfr1Rc8t6UEqhTNN8Yl8OhMq9idC OUkFJTOu8aJEH16iajD3jt8dTV51n6PDAj57s5WW6B+W+QaO8+c+gGeHVuwm4Lmk/DSqA7AEi81Cl UncMAun5PjoNTSZUZzmqUtS8j8fowmcifrwLlRcsWWfNhYX+YuGfzYVV+e/Kri4YxoQewkvDHMDGv Lm0Hnnnj3TVXzQyCyBTnNCY6cTlzXqxT1AGI3g+zWo6TmUYKE045vQecRQ5rjR3xUGmEWkdrRSJfn tAXfOAvQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mbGjD-005WWo-Bs; Fri, 15 Oct 2021 06:30:03 +0000 Date: Thu, 14 Oct 2021 23:30:03 -0700 From: Christoph Hellwig To: Shiyang Ruan Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, nvdimm@lists.linux.dev, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, djwong@kernel.org, dan.j.williams@intel.com, david@fromorbit.com, hch@infradead.org, jane.chu@oracle.com Subject: Re: [PATCH v7 1/8] dax: Use rwsem for dax_{read,write}_lock() Message-ID: References: <20210924130959.2695749-1-ruansy.fnst@fujitsu.com> <20210924130959.2695749-2-ruansy.fnst@fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210924130959.2695749-2-ruansy.fnst@fujitsu.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DCB9AB00009D X-Stat-Signature: jxtdf49aguhuua54axemnqir9pyfe5kz Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=AgLYGCmR; spf=none (imf19.hostedemail.com: domain of BATV+717e4f5ff9d7c10515bf+6627+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+717e4f5ff9d7c10515bf+6627+infradead.org+hch@bombadil.srs.infradead.org; dmarc=none X-HE-Tag: 1634279406-746707 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 Fri, Sep 24, 2021 at 09:09:52PM +0800, Shiyang Ruan wrote: > In order to introduce dax holder registration, we need a write lock for > dax. Because of the rarity of notification failures and the infrequency > of registration events, it would be better to be a global lock rather > than per-device. So, change the current lock to rwsem and introduce a > write lock for registration. I don't think taking the rw_semaphore everywhere will scale, as basically any DAX based I/O will take it (in read mode). So at a minimum we'd need a per-device percpu_rw_semaphore if we want to go there.