should we use atomic instructions to manipulate vmstats.v_wire_count?

Simon 'corecode' Schubert corecode at
Sun Jan 13 05:34:03 PST 2008

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
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:

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.

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