Re: should we use atomic instructions to manipulate vmstats.v_wire_count?

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Nicolas Thery wrote:
> > > I noticed that vmstats.v_wire_count is incremented and decremented w/o
> > > protection.  In contrast, atomic instructions (from <atomic.h>) are
> > > used in freebsd.
> > > Is it a bug in dfly or is it intentional?
> > As far as I understand, we're requiring the mplock for vm operations, so that should be covered.
> Ok but what about zget() called from zalloc() which increments
> v_wire_count?   I reckon zalloc() can be called w/o holding the
> mplock.

I don't think you're allowed to call zalloc() without the mplock.  However there is a comment stating exactly this.  But following the function calls, you could wind up like this:

zalloc
zget
vm_page_alloc or kmem_alloc3
. ..

Now this for sure isn't mp safe.  I believe the comment is wrong, but of course I'm no authority in this area.

cheers
 simon

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