| Message ID | 20210420090925.7457-2-rppt@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: drop pfn_valid_within() and simplify pfn_valid() | expand |
On 20.04.21 11:09, Mike Rapoport wrote: > From: Mike Rapoport <rppt@linux.ibm.com> > > Add comment describing the semantics of pfn_valid() that clarifies that > pfn_valid() only checks for availability of a memory map entry (i.e. struct > page) for a PFN rather than availability of usable memory backing that PFN. > > The most "generic" version of pfn_valid() used by the configurations with > SPARSEMEM enabled resides in include/linux/mmzone.h so this is the most > suitable place for documentation about semantics of pfn_valid(). > > Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > --- > include/linux/mmzone.h | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 47946cec7584..961f0eeefb62 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1410,6 +1410,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > #endif > > #ifndef CONFIG_HAVE_ARCH_PFN_VALID > +/** > + * pfn_valid - check if there is a valid memory map entry for a PFN > + * @pfn: the page frame number to check > + * > + * Check if there is a valid memory map entry aka struct page for the @pfn. > + * Note, that availability of the memory map entry does not imply that > + * there is actual usable memory at that @pfn. The struct page may > + * represent a hole or an unusable page frame. > + * > + * Return: 1 for PFNs that have memory map entries and 0 otherwise > + */ > static inline int pfn_valid(unsigned long pfn) > { > struct mem_section *ms; > I'd rephrase all "there is a valid memory map" to "there is a memory map" and add "pfn_valid() does to indicate whether the memory map as actually initialized -- see pfn_to_online_page()." pfn_valid() means that we can do a pfn_to_page() and don't get a fault when accessing the "struct page". It doesn't state anything about the content.
On Tue, Apr 20, 2021 at 11:22:53AM +0200, David Hildenbrand wrote: > On 20.04.21 11:09, Mike Rapoport wrote: > > From: Mike Rapoport <rppt@linux.ibm.com> > > > > Add comment describing the semantics of pfn_valid() that clarifies that > > pfn_valid() only checks for availability of a memory map entry (i.e. struct > > page) for a PFN rather than availability of usable memory backing that PFN. > > > > The most "generic" version of pfn_valid() used by the configurations with > > SPARSEMEM enabled resides in include/linux/mmzone.h so this is the most > > suitable place for documentation about semantics of pfn_valid(). > > > > Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com> > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > > --- > > include/linux/mmzone.h | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index 47946cec7584..961f0eeefb62 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -1410,6 +1410,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > > #endif > > #ifndef CONFIG_HAVE_ARCH_PFN_VALID > > +/** > > + * pfn_valid - check if there is a valid memory map entry for a PFN > > + * @pfn: the page frame number to check > > + * > > + * Check if there is a valid memory map entry aka struct page for the @pfn. > > + * Note, that availability of the memory map entry does not imply that > > + * there is actual usable memory at that @pfn. The struct page may > > + * represent a hole or an unusable page frame. > > + * > > + * Return: 1 for PFNs that have memory map entries and 0 otherwise > > + */ > > static inline int pfn_valid(unsigned long pfn) > > { > > struct mem_section *ms; > > > > I'd rephrase all "there is a valid memory map" to "there is a memory map" > and add "pfn_valid() does to indicate whether the memory map as actually > initialized -- see pfn_to_online_page()." > > pfn_valid() means that we can do a pfn_to_page() and don't get a fault when > accessing the "struct page". It doesn't state anything about the content. Well, I mean valid in the sense you can access the struct page :) How about: /** * pfn_valid - check if there is a memory map entry for a PFN * @pfn: the page frame number to check * * Check if there is a memory map entry aka struct page for the @pfn and it * is safe to access that struct page; the struct page state may be * uninitialized -- see pfn_to_online_page(). * * Note, that availability of the memory map entry does not imply that * there is actual usable memory at that @pfn. The struct page may * represent a hole or an unusable page frame. * * Return: 1 for PFNs that have memory map entries and 0 otherwise. */
On 20.04.21 14:57, Mike Rapoport wrote: > On Tue, Apr 20, 2021 at 11:22:53AM +0200, David Hildenbrand wrote: >> On 20.04.21 11:09, Mike Rapoport wrote: >>> From: Mike Rapoport <rppt@linux.ibm.com> >>> >>> Add comment describing the semantics of pfn_valid() that clarifies that >>> pfn_valid() only checks for availability of a memory map entry (i.e. struct >>> page) for a PFN rather than availability of usable memory backing that PFN. >>> >>> The most "generic" version of pfn_valid() used by the configurations with >>> SPARSEMEM enabled resides in include/linux/mmzone.h so this is the most >>> suitable place for documentation about semantics of pfn_valid(). >>> >>> Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com> >>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> >>> --- >>> include/linux/mmzone.h | 11 +++++++++++ >>> 1 file changed, 11 insertions(+) >>> >>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>> index 47946cec7584..961f0eeefb62 100644 >>> --- a/include/linux/mmzone.h >>> +++ b/include/linux/mmzone.h >>> @@ -1410,6 +1410,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) >>> #endif >>> #ifndef CONFIG_HAVE_ARCH_PFN_VALID >>> +/** >>> + * pfn_valid - check if there is a valid memory map entry for a PFN >>> + * @pfn: the page frame number to check >>> + * >>> + * Check if there is a valid memory map entry aka struct page for the @pfn. >>> + * Note, that availability of the memory map entry does not imply that >>> + * there is actual usable memory at that @pfn. The struct page may >>> + * represent a hole or an unusable page frame. >>> + * >>> + * Return: 1 for PFNs that have memory map entries and 0 otherwise >>> + */ >>> static inline int pfn_valid(unsigned long pfn) >>> { >>> struct mem_section *ms; >>> >> >> I'd rephrase all "there is a valid memory map" to "there is a memory map" >> and add "pfn_valid() does to indicate whether the memory map as actually >> initialized -- see pfn_to_online_page()." >> >> pfn_valid() means that we can do a pfn_to_page() and don't get a fault when >> accessing the "struct page". It doesn't state anything about the content. > > Well, I mean valid in the sense you can access the struct page :) > How about: > > /** > * pfn_valid - check if there is a memory map entry for a PFN > * @pfn: the page frame number to check > * > * Check if there is a memory map entry aka struct page for the @pfn and it > * is safe to access that struct page; the struct page state may be > * uninitialized -- see pfn_to_online_page(). > * > * Note, that availability of the memory map entry does not imply that > * there is actual usable memory at that @pfn. The struct page may > * represent a hole or an unusable page frame. > * > * Return: 1 for PFNs that have memory map entries and 0 otherwise. > */ > Sounds good to me -- thanks! Reviewed-by: David Hildenbrand <david@redhat.com>
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 47946cec7584..961f0eeefb62 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1410,6 +1410,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) #endif #ifndef CONFIG_HAVE_ARCH_PFN_VALID +/** + * pfn_valid - check if there is a valid memory map entry for a PFN + * @pfn: the page frame number to check + * + * Check if there is a valid memory map entry aka struct page for the @pfn. + * Note, that availability of the memory map entry does not imply that + * there is actual usable memory at that @pfn. The struct page may + * represent a hole or an unusable page frame. + * + * Return: 1 for PFNs that have memory map entries and 0 otherwise + */ static inline int pfn_valid(unsigned long pfn) { struct mem_section *ms;