Date: Mon, 30 May 2011 19:24:15 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: Kostik Belousov <kostikbel@gmail.com>, Rick Macklem <rmacklem@freebsd.org>, svn-src-all@freebsd.org, src-committers@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r222466 - head/sbin/umount Message-ID: <alpine.BSF.2.00.1105301923140.1535@fledge.watson.org> In-Reply-To: <336367081.983085.1306763929731.JavaMail.root@erie.cs.uoguelph.ca> References: <336367081.983085.1306763929731.JavaMail.root@erie.cs.uoguelph.ca>
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On Mon, 30 May 2011, Rick Macklem wrote: > Hehe. I'm so old, I do two syncs, as required by 6th Edition.:-) > > I assumed the sync() was meant to be an optimization (given the comment for > it) in the sense that it would get the writes of dirty blocks started "right > away". However, given the short period of time from the the sync(2) call to > the unmount(2) call, I'm not convinced it makes a significant difference. (I > thought of just getting rid of it, but figured it was harmless for the non > "-f" case and might matter for a buggy fs that doesn't get the unmount(2) > quite right. ie. Same argument as doing the triple-sync, just to be sure.) If it masks, for example, lateny for a synchronous RPC to the remote mountd to deregister the mountpoint, allowing a cache flush and unmount to take place concurrently, that might be a useful benefit. I'm not sure I see any evidence that is the case in the source code, however. Robert
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