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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>