On Fri, 26 Feb 2021, Andrew Morton wrote:
> On Fri, 26 Feb 2021 12:17:20 -0800 Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> > From: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> >
> > This is only useful under CONFIG_NUMA. IIUC skipping the check is the
> > right thing to do here, as without CONFIG_NUMA there will never be any
> > large node distances on non-NUMA systems.
> >
> > I expected this to manifest as a link failure under (!CONFIG_NUMA &&
> > CONFIG_TRANSPARENT_HUGE_PAGES), but I'm not actually seeing that. I
> > think the reference is just getting pruned before it's checked, but I
> > didn't get that from reading the code so I'm worried I'm missing
> > something.
> >
> > Either way, this is necessary to guard the definition of
> > node_reclaim_distance with CONFIG_NUMA.
> >
> > Signed-off-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> > ---
> > mm/khugepaged.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index a7d6cb912b05..b1bf191c3a54 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -819,8 +819,10 @@ static bool khugepaged_scan_abort(int nid)
> > for (i = 0; i < MAX_NUMNODES; i++) {
> > if (!khugepaged_node_load[i])
> > continue;
> > +#ifdef CONFIG_NUMA
> > if (node_distance(nid, i) > node_reclaim_distance)
> > return true;
> > +#endif
> > }
> > return false;
> > }
>
> This makes the entire loop a no-op. Perhaps Kirill can help take a
> look at removing unnecessary code in khugepaged.c when CONFIG_NUMA=n?
First lines of khugepaged_scan_abort() say
if (!node_reclaim_mode)
return false;
And include/linux/swap.h says
#ifdef CONFIG_NUMA
extern int node_reclaim_mode;
extern int sysctl_min_unmapped_ratio;
extern int sysctl_min_slab_ratio;
#else
#define node_reclaim_mode 0
#endif
So, no need for an #ifdef CONFIG_NUMA inside khugepaged_scan_abort().
Hugh
