Date: Tue, 28 Dec 1999 01:44:15 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Proposed patch to fix VN device (again) Message-ID: <8502.946341855@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 27 Dec 1999 16:26:59 PST." <199912280026.QAA34572@apollo.backplane.com>
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In message <199912280026.QAA34572@apollo.backplane.com>, Matthew Dillon writes: > VN calls vm_pager_strategy() which collects I/O in filesystem buffers > (bp)'s in order to cluster the I/O, and you cannot initiate I/O on > filesystem buffers without a valid b_dev. > > So, the jist of the problem is that in order to get reasonable performance > out of the thing (i.e. not issue 4K I/O's to the disk), we have to use > filesystem buffers which means the bp must be properly initialized. vm_pager_strategy() branches out based on the object type and ends up in swap_pager_strategy() which only uses b_dev after calling swstrategy() then only in a diagnostic printf which we had better never reach. swstrategy() which initializes bp->b_dev to the right physical device. I'm afraid I don't see why or where we would need the bogus /dev/drum dev_t. Furthermore, since we have already clustered above the VN device, I seriously doubt the utility of doing it again between VN and the swapdevice. -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." FreeBSD -- It will take a long time before progress goes too far! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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