On Wed, Jul 17, 2013 at 05:58:13PM -0700, Hugh Dickins wrote:
> On Wed, 17 Jul 2013, Dave Hansen wrote:
> > On 07/17/2013 02:09 PM, Andrew Morton wrote:
> > > lock_page() is a pretty commonly called function, and I assume quite a
> > > lot of people run with CONFIG_DEBUG_VM=y.
> > >
> > > Is the overhead added by this patch really worthwhile?
> >
> > I always thought of it as a developer-only thing. I don't think any of
> > the big distros turn it on by default.
>
> That's how I think of it too (and the problem is often that too few mm
> developers turn it on); but Dave Jones did confirm last November that
> Fedora turns it on.
>
> I believe Fedora turns it on to help us all, and wouldn't mind a mere
> VM_BUG_ON(PageTail(page)) in __lock_page() if it's helpful to Kirill.
>
> But if VM_BUG_ONs become expensive, I do think it's for Fedora to
> turn off CONFIG_DEBUG_VM, rather than for mm developers to avoid it.
I'm ambivalent about whether we keep it on or off, we have no shortage
of bugs to fix already, though I think as mentioned above, very few people
actually enable it, so we're going to lose a lot of testing.
Another idea, perhaps is an extra config option for more expensive debug
options ?
Dave
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