Date: Mon, 10 Jul 2017 10:57:22 -0500 (CDT) From: "Valeri Galtsev" <galtsev@kicp.uchicago.edu> To: "Steve O'Hara-Smith" <steve@sohara.org> Cc: freebsd-questions@freebsd.org Subject: Re: Unusual Question Message-ID: <60058.128.135.52.6.1499702242.squirrel@cosmo.uchicago.edu> In-Reply-To: <20170710163351.a347713b6d8f64e141d1d9f2@sohara.org> References: <888578F8-AD68-4993-823C-152789F3C929@mail.sermon-archive.info> <52627.76.193.16.95.1499645892.squirrel@cosmo.uchicago.edu> <BF16E1CF-A889-4734-981E-2B68115FCD3C@mail.sermon-archive.info> <20170710052228.GA2338@c720-r314251> <20170710090547.15ee3afc07c09955ba621ae1@sohara.org> <26749.128.135.52.6.1499700385.squirrel@cosmo.uchicago.edu> <20170710163351.a347713b6d8f64e141d1d9f2@sohara.org>
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On Mon, July 10, 2017 10:33 am, Steve O'Hara-Smith wrote: > On Mon, 10 Jul 2017 10:26:25 -0500 (CDT) > "Valeri Galtsev" <galtsev@kicp.uchicago.edu> wrote: > >> I believe, the kernel addresses swap not by addressing sectors on raw >> device covering the whole physical drive, but as "relative sectors" >> through swap partition device. > > Sure, but I doubt it reads the partition table again after it has > it read the first time, that's an obvious thing to cache. > >> If I'm right, once drive partition table is >> gone reading swap will fail and panic kernel. > > I doubt it, the partition table should be cached in memory, > otherwise yes that would panic the kernel, but reading the partition table > every time a page needs swapping in would be stupidly inefficient so I > don't believe it happens. I agree, it will be inefficient if it were programmed that way... however, whenever I add partition with gpart, partition table gets re-read, and new device gets created. That is what probably confused me (as gpart may trigger kernel re-read partition table, whereas dd unlikely will). Valeri > >> But the suggestion you made in another post: to make > > Not my suggestion, it's a sensible one but I don't think it's > needed. > > -- > Steve O'Hara-Smith | Directable Mirror Arrays > C:>WIN | A better way to focus the > sun > The computer obeys and wins. | licences available see > You lose and Bill collects. | http://www.sohara.org/ > _______________________________________________ > freebsd-questions@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to > "freebsd-questions-unsubscribe@freebsd.org" > ++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++
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