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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7acde62b3d0sm158399585a.134.2024.09.25.03.46.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Sep 2024 03:46:37 -0700 (PDT) Received: from phl-compute-02.internal (phl-compute-02.phl.internal [10.202.2.42]) by mailfauth.phl.internal (Postfix) with ESMTP id 0FF831200069; Wed, 25 Sep 2024 06:46:37 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-02.internal (MEProxy); Wed, 25 Sep 2024 06:46:37 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeftddrvddthedgfedvucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggvpdfu rfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnh htshculddquddttddmnecujfgurhepfffhvfevuffkfhggtggujgesthdtredttddtvden ucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrd gtohhmqeenucggtffrrghtthgvrhhnpeehudfgudffffetuedtvdehueevledvhfelleei vedtgeeuhfegueevieduffeivdenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmh epmhgrihhlfhhrohhmpegsohhquhhnodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhi thihqdeiledvgeehtdeigedqudejjeekheehhedvqdgsohhquhhnrdhfvghngheppehgmh grihhlrdgtohhmsehfihigmhgvrdhnrghmvgdpnhgspghrtghpthhtohepvdejpdhmohgu vgepshhmthhpohhuthdprhgtphhtthhopehjohhnrghsrdhosggvrhhhrghushgvrheshh hurgifvghitghlohhuugdrtghomhdprhgtphhtthhopehlihhnuhigqdhkvghrnhgvlhes vhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehrtghusehvghgvrhdrkhgvrh hnvghlrdhorhhgpdhrtghpthhtoheplhhinhhugidqmhhmsehkvhgrtghkrdhorhhgpdhr tghpthhtoheplhhkmhhmsehlihhsthhsrdhlihhnuhigrdguvghvpdhrtghpthhtohepph gruhhlmhgtkheskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepfhhrvgguvghrihgtsehk vghrnhgvlhdrohhrghdprhgtphhtthhopehnvggvrhgrjhdruhhprgguhhihrgihsehkvg hrnhgvlhdrohhrghdprhgtphhtthhopehjohgvlhesjhhovghlfhgvrhhnrghnuggvshdr ohhrgh X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 25 Sep 2024 06:46:36 -0400 (EDT) Date: Wed, 25 Sep 2024 03:45:54 -0700 From: Boqun Feng To: Jonas Oberhauser Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev, "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Mark Rutland , Thomas Gleixner , Kent Overstreet , Linus Torvalds , Vlastimil Babka , maged.michael@gmail.com, Neeraj Upadhyay Subject: Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers Message-ID: References: <20240917143402.930114-1-boqun.feng@gmail.com> <20240917143402.930114-2-boqun.feng@gmail.com> <55975a55-302f-4c45-bfcc-192a8a1242e9@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: 55hpe7tjh3gwxjg171b1p1ng1nrmeifw X-Rspamd-Queue-Id: 9B3D9A0005 X-Rspamd-Server: rspam11 X-HE-Tag: 1727261199-682279 X-HE-Meta: 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 OzSMCM6k EPXyJDNtZorh1VepYIPFUO+F3As53fx5JvyHHc3Yamy/35Fw01yPR5ZW9fhma5FwXPOduc+3BcnR00PTek7KuJWV6VxByTAy4wd0UMX5wVowwvTPVRqmIqq98Cgz0tegh74ufxQHUnUpWgyHZOscOzqrVQcmvyU5DSuRJmZi+5b08kemfg5MCjU9KYAROf5a2QigZ4QnNzeTmt7lvPSFYVxIIKGtuaFDnSYrC9XsoFUy1PZSX+1SIPv0WOnpHkwA1fAzZet2KXEPhAdGpwyD0KBTHRnDFjZgBBDS7KbZCDP5MLGVqYvEy7OGy+nLBFWBRsrpPqB4DGqV6FKV4qlRX28ExihrblnzQpK2NXdTqXeCyW7lkLl/XLtw+q/FCxkOgPdvInIi4Ft+vyUNwsrW+TFLOPXQdP7E9nmNUKL7myhfdpyi+pmDNINAlbO28L4EgMlyyfqvwEl15y5WLNwhpoDi28BsnRPeRryn0 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, Sep 25, 2024 at 12:11:52PM +0200, Jonas Oberhauser wrote: > > > Am 9/25/2024 um 12:02 PM schrieb Boqun Feng: > > Hi Jonas, > > > > Of > > course, if we are really worried about compilers being too "smart" > > Ah, I see you know me better and better... > > > we can always do the comparison in asm code, then compilers don't know > > anything of the equality between 'ptr' and 'head - head_offset'. > Yes, but then a simple compiler barrier between the comparison and returning > ptr would also do the trick, right? And maybe easier on the eyes. > The thing about putting a compiler barrier is that it will prevent all compiler reorderings, and some of the reordering may contribute to better codegen. (I know in this case, we have a smp_mb(), but still compilers can move unrelated code upto the second load for optimization purpose). Asm comparison is cheaper in this way. But TBH, compilers should provide a way to compare pointer values without using the result for pointer equality proof, if "convert to unsigned long" doesn't work, some other ways should work. Regards, Boqun > > Have fun, > jonas >