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Message-ID: <20080219025643.GD4066@agk.fab.redhat.com> Date: Tue, 19 Feb 2008 02:56:43 +0000 From: Alasdair G Kergon <agk@...hat.com> To: David Chinner <dgc@....com> Cc: Michael Tokarev <mjt@....msk.ru>, Ric Wheeler <ric@....com>, device-mapper development <dm-devel@...hat.com>, Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org Subject: Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices On Tue, Feb 19, 2008 at 09:16:44AM +1100, David Chinner wrote: > Surely any hardware that doesn't support barrier > operations can emulate them with cache flushes when they receive a > barrier I/O from the filesystem.... My complaint about having to support them within dm when more than one device is involved is because any efficiencies disappear: you can't send further I/O to any one device until all the other devices have completed their barrier (or else later I/O to that device could overtake the barrier on another device). And then I argue that it would be better for the filesystem to have the information that these are not hardware barriers so it has the opportunity of tuning its behaviour (e.g. flushing less often because it's a more expensive operation). Alasdair -- agk@...hat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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