[RESEND PATCH v2] mm/sparse: clarify pgdat_to_phys

[RESEND PATCH v2] mm/sparse: clarify pgdat_to_phys

[Miles Chen]

Clarify pgdat_to_phys() by testing if
pgdat == &contig_page_data when CONFIG_NUMA=n.

contig_page_data is only available when CONFIG_NUMA=n
so we have to use #ifndef here.

No functional change intended.

Comment from Mark [1]:
"
... and I reckon it'd be clearer and more robust to define
pgdat_to_phys() in the same ifdefs as contig_page_data so
that these, stay in-sync. e.g. have:

| #ifdef CONFIG_NUMA
| #define pgdat_to_phys(x)	virt_to_phys(x)
| #else /* CONFIG_NUMA */
|
| extern struct pglist_data contig_page_data;
| ...
| #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
|
| #endif /* CONIFIG_NUMA */
"

Comment from Mike [2]:
"
I'm not sure a macro is better than a static inline.

Maybe we'd want to warn if pgdat passed to pgtat_to_phys() is not
&contig_page_data, e.g something like

static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
{
	if (!IS_ENABLED(CONFIG_NUMA)) {
		if (pgdat == &contig_page_data)
			return __pa_symbol(&contig_page_data);
		else
			pr_warn("Unexpected pglist_data pointer!\n");
	}

	return __pa(pgdat);
}
"

[1] https://lore.kernel.org/linux-arm-kernel/20210615131902.GB47121@C02TD0UTHF1T.local/
[2] https://lore.kernel.org/patchwork/patch/1452903/#1650759

Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>

---

Change since v1:
Thanks for Mike's comment, check if pgdat == &contig_page_data,
so it is clearer that we only expect contig_page_data when
CONFIG_NUMA=n.
---
 mm/sparse.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 6326cdf36c4f..f73ff3c124c5 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -348,10 +348,11 @@ size_t mem_section_usage_size(void)
 static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
 {
 #ifndef CONFIG_NUMA
-	return __pa_symbol(pgdat);
-#else
+	if (pgdat == &contig_page_data)
+		return __pa_symbol(&contig_page_data);
+	pr_warn("Unexpected pglist_data pointer!\n");
+#endif /* !CONFIG_NUMA */
 	return __pa(pgdat);
-#endif
 }
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
-- 
2.18.0

Re: [RESEND PATCH v2] mm/sparse: clarify pgdat_to_phys

[David Hildenbrand]

On 23.07.21 09:01, Miles Chen wrote:
> Clarify pgdat_to_phys() by testing if
> pgdat == &contig_page_data when CONFIG_NUMA=n.
> 
> contig_page_data is only available when CONFIG_NUMA=n
> so we have to use #ifndef here.
> 
> No functional change intended.
> 
> Comment from Mark [1]:
> "
> ... and I reckon it'd be clearer and more robust to define
> pgdat_to_phys() in the same ifdefs as contig_page_data so
> that these, stay in-sync. e.g. have:
> 
> | #ifdef CONFIG_NUMA
> | #define pgdat_to_phys(x)	virt_to_phys(x)
> | #else /* CONFIG_NUMA */
> |
> | extern struct pglist_data contig_page_data;
> | ...
> | #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
> |
> | #endif /* CONIFIG_NUMA */
> "
> 
> Comment from Mike [2]:
> "
> I'm not sure a macro is better than a static inline.
> 
> Maybe we'd want to warn if pgdat passed to pgtat_to_phys() is not
> &contig_page_data, e.g something like
> 
> static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> {
> 	if (!IS_ENABLED(CONFIG_NUMA)) {
> 		if (pgdat == &contig_page_data)
> 			return __pa_symbol(&contig_page_data);
> 		else
> 			pr_warn("Unexpected pglist_data pointer!\n");
> 	}
> 
> 	return __pa(pgdat);
> }
> "
> 
> [1] https://lore.kernel.org/linux-arm-kernel/20210615131902.GB47121@C02TD0UTHF1T.local/
> [2] https://lore.kernel.org/patchwork/patch/1452903/#1650759
> 
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> 
> ---
> 
> Change since v1:
> Thanks for Mike's comment, check if pgdat == &contig_page_data,
> so it is clearer that we only expect contig_page_data when
> CONFIG_NUMA=n.
> ---
>   mm/sparse.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 6326cdf36c4f..f73ff3c124c5 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -348,10 +348,11 @@ size_t mem_section_usage_size(void)
>   static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
>   {
>   #ifndef CONFIG_NUMA
> -	return __pa_symbol(pgdat);
> -#else
> +	if (pgdat == &contig_page_data)
> +		return __pa_symbol(&contig_page_data);
> +	pr_warn("Unexpected pglist_data pointer!\n");

Shouldn't this rather be a VM_BUG_ON()?

Because it looks like something that should barely happen and we might 
not want to perform runtime checks on each and every system?


-- 
Thanks,

David / dhildenb

Re: [RESEND PATCH v2] mm/sparse: clarify pgdat_to_phys

[Miles Chen]

On Fri, 2021-07-23 at 09:10 +0200, David Hildenbrand wrote:
> On 23.07.21 09:01, Miles Chen wrote:
> > Clarify pgdat_to_phys() by testing if
> > pgdat == &contig_page_data when CONFIG_NUMA=n.
> > 
> > contig_page_data is only available when CONFIG_NUMA=n
> > so we have to use #ifndef here.
> > 
> > No functional change intended.
> > 
> > Comment from Mark [1]:
> > "
> > ... and I reckon it'd be clearer and more robust to define
> > pgdat_to_phys() in the same ifdefs as contig_page_data so
> > that these, stay in-sync. e.g. have:
> > 
> > | #ifdef CONFIG_NUMA
> > | #define pgdat_to_phys(x)	virt_to_phys(x)
> > | #else /* CONFIG_NUMA */
> > |
> > | extern struct pglist_data contig_page_data;
> > | ...
> > | #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
> > |
> > | #endif /* CONIFIG_NUMA */
> > "
> > 
> > Comment from Mike [2]:
> > "
> > I'm not sure a macro is better than a static inline.
> > 
> > Maybe we'd want to warn if pgdat passed to pgtat_to_phys() is not
> > &contig_page_data, e.g something like
> > 
> > static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> > {
> > 	if (!IS_ENABLED(CONFIG_NUMA)) {
> > 		if (pgdat == &contig_page_data)
> > 			return __pa_symbol(&contig_page_data);
> > 		else
> > 			pr_warn("Unexpected pglist_data pointer!\n");
> > 	}
> > 
> > 	return __pa(pgdat);
> > }
> > "
> > 
> > [1] https://urldefense.com/v3/__https://lore.kernel.org/linux-arm-kernel/20210615131902.GB47121@C02TD0UTHF1T.local/__;!!CTRNKA9wMg0ARbw!1bJTnH2gJ6QvsBKTXH8xOiKfHF-xq_1dok3cnETD4e4qjryntFm8K0XjtEmkHAxG6g$ 
> > [2] https://urldefense.com/v3/__https://lore.kernel.org/patchwork/patch/1452903/*1650759__;Iw!!CTRNKA9wMg0ARbw!1bJTnH2gJ6QvsBKTXH8xOiKfHF-xq_1dok3cnETD4e4qjryntFm8K0XjtEmbGXEkVg$ 
> > 
> > Cc: Mike Rapoport <rppt@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> > 
> > ---
> > 
> > Change since v1:
> > Thanks for Mike's comment, check if pgdat == &contig_page_data,
> > so it is clearer that we only expect contig_page_data when
> > CONFIG_NUMA=n.
> > ---
> >   mm/sparse.c | 7 ++++---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 6326cdf36c4f..f73ff3c124c5 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -348,10 +348,11 @@ size_t mem_section_usage_size(void)
> >   static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> >   {
> >   #ifndef CONFIG_NUMA
> > -	return __pa_symbol(pgdat);
> > -#else
> > +	if (pgdat == &contig_page_data)
> > +		return __pa_symbol(&contig_page_data);
> > +	pr_warn("Unexpected pglist_data pointer!\n");
> 
> Shouldn't this rather be a VM_BUG_ON()?
> 
> Because it looks like something that should barely happen and we might 
> not want to perform runtime checks on each and every system?

thanks for your comment, I will use VM_BUG_ON() to check if pgdat ==
contig_page_data to avoid the runtime check.
> 
>