Re: [PATCH 3/3] Add timeout feature

Pavel Machek
2008-07-08T23:18:38Z

On Wed 2008-07-09 09:10:27, Dave Chinner wrote:
> On Mon, Jul 07, 2008 at 01:07:31PM +0200, Pavel Machek wrote:
> > Hi!
> >
> > > I still disagree with this whole patch. There is not reason to let
> > > the freeze request timeout - an auto-unfreezing will only confuse the
> > > hell out of the caller. The only reason where the current XFS freeze
> > > call can hang and this would be theoretically useful is when the
> >
> > What happens when someone dirties so much data that vm swaps out
> > whatever process that frozen the filesystem?
>
> a) you can't dirty a frozen filesystem - by definition a frozen
> filesystem is a *clean filesystem* and *cannot be dirtied*.

Can you stop me?

mmap("/some/huge_file", MAP_SHARED);

then write to memory mapping?

> b) Swap doesn't write through the filesystem
> c) you can still read from a frozen filesystem to page your
> executable?? in.

atime modification should mean dirty data, right? And dirty data mean
memory pressure, right?

> d) if dirtying another unfrozen filesystem swaps out your
~~~~~~~
> application so it can't run, then there's a major VM bug.
> Regardless, until the app completes it is relying on the
> filesystem being frozen, so it better remain frozen....

Agreed. With emphasis on "another".

> > I though that was why the timeout was there...
>
> Not that I know of.

Ok, lets see how you deal with mmap.
Pavel

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