svn commit: r222466 - head/sbin/umount
Robert Watson
rwatson at FreeBSD.org
Mon May 30 18:24:16 UTC 2011
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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