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[209.85.218.54]) by smtp.gmail.com with ESMTPSA id r2-20020a170906350200b0098e34446464sm416084eja.25.2023.11.01.15.24.03 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Nov 2023 15:24:03 -0700 (PDT) Received: by mail-ej1-f54.google.com with SMTP id a640c23a62f3a-99357737980so44069066b.2 for ; Wed, 01 Nov 2023 15:24:03 -0700 (PDT) X-Received: by 2002:a17:906:ee8b:b0:9be:263b:e31e with SMTP id wt11-20020a170906ee8b00b009be263be31emr2561024ejb.33.1698877442973; Wed, 01 Nov 2023 15:24:02 -0700 (PDT) MIME-Version: 1.0 References: <2ef9ac6180e47bc9cc8edef20648a000367c4ed2.camel@kernel.org> <6df5ea54463526a3d898ed2bd8a005166caa9381.camel@kernel.org> <3d6a4c21626e6bbb86761a6d39e0fafaf30a4a4d.camel@kernel.org> <20231101101648.zjloqo5su6bbxzff@quack3> <3ae88800184f03b152aba6e4a95ebf26e854dd63.camel@hammerspace.com> In-Reply-To: <3ae88800184f03b152aba6e4a95ebf26e854dd63.camel@hammerspace.com> From: Linus Torvalds Date: Wed, 1 Nov 2023 12:23:44 -1000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC 2/9] timekeeping: new interfaces for multigrain timestamp handing To: Trond Myklebust Cc: Jan Kara , Chris Mason , Josef Bacik , John Stultz , "Darrick J. Wong" , Christian Brauner , Chandan Babu R , Hugh Dickins , linux-xfs , Dave Chinner , Andrew Morton , dsterba@suse.com, Linux Kernel Mailing List , Jeff Layton , Thomas Gleixner , Linux-MM , "open list:NFS, SUNRPC, AND..." , "Theodore Ts'o" , Al Viro , Ext4 Developers List , Amir Goldstein , linux-btrfs , linux-fsdevel , Andreas Dilger , Kent Overstreet , Stephen Boyd , David Howells , Jan Kara Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: ya7h13nuzjqccy1nitkrx1jok4kdcoou X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 50EF88001F X-Rspam-User: X-HE-Tag: 1698877445-152830 X-HE-Meta: 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 XBgRN2Gx 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 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, Nov 1, 2023, 11:35 Trond Myklebust wrote: > > My client writes to the file and immediately reads the ctime. A 3rd > party client then writes immediately after my ctime read. > A reboot occurs (maybe minutes later), then I re-read the ctime, and > get the same value as before the 3rd party write. > > Yes, most of the time that is better than the naked ctime, but not > across a reboot. Ahh, I knew I was missing something. But I think it's fixable, with an additional rule: - when generating STATX_CHANGE_COOKIE, if the ctime matches the current time and the ctime counter is zero, set the ctime counter to 1. That means that you will have *spurious* cache invalidations of such cached data after a reboot, but only for reads that happened right after the file was written. Now, it's obviously not unheard of to finish writing a file, and then immediately reading the results again. But at least those caches should be somewhat limited (and the problem then only happens when the nfs server is rebooted). I *assume* that the whole thundering herd issue with lots of clients tends to be for stable files, not files that were just written and then immediately cached? I dunno. I'm sure there's still some thinko here. Linus