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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t18PC-00000008eF5-3kB5; Wed, 16 Oct 2024 18:05:55 +0000 Date: Wed, 16 Oct 2024 19:05:54 +0100 From: Matthew Wilcox To: Waiman Long Cc: lizhe.67@bytedance.com, peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC 1/2] rwsem: introduce upgrade_read interface Message-ID: References: <20241016043600.35139-1-lizhe.67@bytedance.com> <20241016043600.35139-2-lizhe.67@bytedance.com> <7f7b277a-7019-4bf4-b100-0505c6ce9737@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7f7b277a-7019-4bf4-b100-0505c6ce9737@redhat.com> X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 7408010001B X-Stat-Signature: 1ashi6hqo73q7s4ni8nou7qtu39pz57a X-HE-Tag: 1729101951-903326 X-HE-Meta: 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 wXQ40mME lxuAc6PNQHXu8auRrwL1PTwJTNoCceU/0IO3bthw1FrsoGTiroNChyz66kmevO8HMTLvlrmIyPW2DRv0quAphH0gTkcCtUehZsaRTZL1ufkxm0VtPcCWmOuavq1BTyz5XEidS1VLnvW3igKc+M1pUgkmKQ95/U60htXntmKrGUY7ujNsxREtjQOxDepa3AU1axNUErxKo7K1RcmUIU6ub8vlJ537vh5E15O7Te4y+KHgnYYVQK/PatoBhpZbBHGHY0P3QaX8MrgbA3PHr+TM7m+QNdkGkbsrKmAyhLps3oKtP/yCEMc0mRuMbLChofm15+usv+qaNMr3lWpimtn2PGq9ynL+y0Yd1aaJr 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: List-Subscribe: List-Unsubscribe: On Wed, Oct 16, 2024 at 10:23:14AM -0400, Waiman Long wrote: > Another alternative that I have been thinking about is a down_read() variant > with intention to upgrade later. This will ensure that only one active > reader is allowed to upgrade later. With this, upgrade_read() will always > succeed, maybe with some sleeping, as long as the correct down_read() is > used. How is that different from Kent's SIX locks other than you can take an rwsem for write immediately (SIX locks have to be taken for Intent and then Upgraded)?