On Thu, 2007-12-20 at 13:14 +0000, Hugh Dickins wrote:
> On Wed, 19 Dec 2007, Dave Hansen wrote:
> > > ---
> > > linux-2.6.24-rc5/mm/page_alloc.c~memory-controller-move-to-bug-on-in-free_hot_cold_page
> > > 2007-12-19 11:31:46.000000000 +0530
> > > +++ linux-2.6.24-rc5-balbir/mm/page_alloc.c 2007-12-19
> > > 11:33:45.000000000 +0530
> > > @@ -995,7 +995,7 @@ static void fastcall free_hot_cold_page(
> > >
> > > if (!PageHighMem(page))
> > > debug_check_no_locks_freed(page_address(page), PAGE_SIZE);
> > > - page_assign_page_cgroup(page, NULL);
> > > + VM_BUG_ON(page_get_page_cgroup(page));
> > > arch_free_page(page, 0);
> > > kernel_map_pages(page, 1, 0);
> >
> > Hi Balbir,
> >
> > You generally want to do these like:
> >
> > foo = page_assign_page_cgroup(page, NULL);
> > VM_BUG_ON(foo);
> >
> > Some embedded people have been known to optimize kernel size like this:
> >
> > #define VM_BUG_ON(x) do{}while(0)
>
> Balbir's patch looks fine to me: I don't get your point there, Dave.
There was a lengthy discussion here:
http://lkml.org/lkml/2007/12/14/131
on the merit of debug statements with side effects. But looking at our
definition:
#ifdef CONFIG_DEBUG_VM
#define VM_BUG_ON(cond) BUG_ON(cond)
#else
#define VM_BUG_ON(condition) do { } while(0)
#endif
disabling CONFIG_DEBUG_VM breaks the code as proposed by Balbir in that
it will no longer acquire the reference.
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