On Fri, 27 Apr 2007, Linus Torvalds wrote:
>
> The "let's stop all kernel threads" is superstition. It's the same kind of
> superstition that made people write "sync" three times before turning off
> the power in the olden times. It's the kind of superstition that comes
> from "we don't do things right, so let's be vewy vewy quiet and _pray_
> that it works when we are beign quiet".
Side note: while I think things should probably *work* even with user
processes going full bore while a snapshot it taken, I'll freely admit
that I'll follow that superstition far enough that I think it's probably a
good idea to try to quiesce the system to _some_ degree, and that stopping
user programs is a good idea. Partly because the whole memory shrinking
thing, and partly just because we should do the snapshot with hw IO queues
empty.
But I don't think it would necessarily be wrong (and in many ways it would
probably be *right*) to do that IO queue stopping at the queue level
rather than at a process level. Why stop processes just becasue you want
to clean out IO queues? They are two totally different things!
Linus
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