Re: [PATCH 1/2] mm: Guard a use of node_reclaim_distance with CONFIFG_NUMA
From: Hugh Dickins
Date: Fri Feb 26 2021 - 20:32:53 EST
On 2021年2月26日, Andrew Morton wrote:
>
On 2021年2月26日 12:17:20 -0800 Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
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> 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
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> think the reference is just getting pruned before it's checked, but I
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> 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 ++
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> 1 file changed, 2 insertions(+)
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>
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
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> index a7d6cb912b05..b1bf191c3a54 100644
>
> --- a/mm/khugepaged.c
>
> +++ b/mm/khugepaged.c
>
> @@ -819,8 +819,10 @@ static bool khugepaged_scan_abort(int nid)
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> for (i = 0; i < MAX_NUMNODES; i++) {
>
> if (!khugepaged_node_load[i])
>
> continue;
>
> +#ifdef CONFIG_NUMA
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> if (node_distance(nid, i) > node_reclaim_distance)
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> return true;
>
> +#endif
>
> }
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> 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