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?
