Messages in this thread | | | Date | Wed, 17 Jul 2013 17:58:13 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [PATCH 5/8] thp, mm: locking tail page is a bug |
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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.
Hugh
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