| Message ID | 20230711044834.72809-6-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add support for memmap on memory feature on ppc64 | expand |
On 11.07.23 06:48, Aneesh Kumar K.V wrote: > Radix vmemmap mapping can map things correctly at the PMD level or PTE > level based on different device boundary checks. Hence we skip the > restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also > makes the feature widely useful because to use PMD_SIZE vmemmap area we > require a memory block size of 2GiB > > We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature > can work with a memory block size of 256MB. Using altmap.reserve feature > to align things correctly at pageblock granularity. We can end up > losing some pages in memory with this. For ex: with a 256MiB memory block > size, we require 4 pages to map vmemmap pages, In order to align things > correctly we end up adding a reserve of 28 pages. ie, for every 4096 > pages 28 pages get reserved. > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > --- > arch/powerpc/Kconfig | 1 + > arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++ > .../platforms/pseries/hotplug-memory.c | 3 +- > mm/memory_hotplug.c | 2 ++ > 4 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 116d6add0bb0..f890907e5bbf 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -157,6 +157,7 @@ config PPC > select ARCH_HAS_UBSAN_SANITIZE_ALL > select ARCH_HAVE_NMI_SAFE_CMPXCHG > select ARCH_KEEP_MEMBLOCK > + select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU > select ARCH_MIGHT_HAVE_PC_PARPORT > select ARCH_MIGHT_HAVE_PC_SERIO > select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX > diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h > index 68817ea7f994..8e6c92dde6ad 100644 > --- a/arch/powerpc/include/asm/pgtable.h > +++ b/arch/powerpc/include/asm/pgtable.h > @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x) > int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size); > bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start, > unsigned long page_size); > +/* > + * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details > + * some of the restrictions. We don't check for PMD_SIZE because our > + * vmemmap allocation code can fallback correctly. The pageblock > + * alignment requirement is met using altmap->reserve blocks. > + */ > +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory > +static inline bool arch_supports_memmap_on_memory(unsigned long size) > +{ > + unsigned long nr_pages = size >> PAGE_SHIFT; > + unsigned long vmemmap_size = nr_pages * sizeof(struct page); > + > + if (!radix_enabled()) > + return false; > + > +#ifdef CONFIG_PPC_4K_PAGES > + return IS_ALIGNED(vmemmap_size, PMD_SIZE); > +#else > + /* > + * Make sure the vmemmap allocation is fully contianed > + * so that we always allocate vmemmap memory from altmap area. > + * The pageblock alignment requirement is met by using > + * reserve blocks in altmap. > + */ > + return IS_ALIGNED(vmemmap_size, PAGE_SIZE); Can we move that check into common code as well? If our (original) vmemmap size would not fit into a single page, we would be in trouble on any architecture. Did not check if it would be an issue for arm64 as well in case we would allow eventually wasting memory.
On 7/11/23 8:56 PM, David Hildenbrand wrote: > On 11.07.23 06:48, Aneesh Kumar K.V wrote: >> Radix vmemmap mapping can map things correctly at the PMD level or PTE >> level based on different device boundary checks. Hence we skip the >> restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also >> makes the feature widely useful because to use PMD_SIZE vmemmap area we >> require a memory block size of 2GiB >> >> We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature >> can work with a memory block size of 256MB. Using altmap.reserve feature >> to align things correctly at pageblock granularity. We can end up >> losing some pages in memory with this. For ex: with a 256MiB memory block >> size, we require 4 pages to map vmemmap pages, In order to align things >> correctly we end up adding a reserve of 28 pages. ie, for every 4096 >> pages 28 pages get reserved. >> >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> >> --- >> arch/powerpc/Kconfig | 1 + >> arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++ >> .../platforms/pseries/hotplug-memory.c | 3 +- >> mm/memory_hotplug.c | 2 ++ >> 4 files changed, 33 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >> index 116d6add0bb0..f890907e5bbf 100644 >> --- a/arch/powerpc/Kconfig >> +++ b/arch/powerpc/Kconfig >> @@ -157,6 +157,7 @@ config PPC >> select ARCH_HAS_UBSAN_SANITIZE_ALL >> select ARCH_HAVE_NMI_SAFE_CMPXCHG >> select ARCH_KEEP_MEMBLOCK >> + select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU >> select ARCH_MIGHT_HAVE_PC_PARPORT >> select ARCH_MIGHT_HAVE_PC_SERIO >> select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX >> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h >> index 68817ea7f994..8e6c92dde6ad 100644 >> --- a/arch/powerpc/include/asm/pgtable.h >> +++ b/arch/powerpc/include/asm/pgtable.h >> @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x) >> int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size); >> bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start, >> unsigned long page_size); >> +/* >> + * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details >> + * some of the restrictions. We don't check for PMD_SIZE because our >> + * vmemmap allocation code can fallback correctly. The pageblock >> + * alignment requirement is met using altmap->reserve blocks. >> + */ >> +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory >> +static inline bool arch_supports_memmap_on_memory(unsigned long size) >> +{ >> + unsigned long nr_pages = size >> PAGE_SHIFT; >> + unsigned long vmemmap_size = nr_pages * sizeof(struct page); >> + >> + if (!radix_enabled()) >> + return false; >> + >> +#ifdef CONFIG_PPC_4K_PAGES >> + return IS_ALIGNED(vmemmap_size, PMD_SIZE); >> +#else >> + /* >> + * Make sure the vmemmap allocation is fully contianed >> + * so that we always allocate vmemmap memory from altmap area. >> + * The pageblock alignment requirement is met by using >> + * reserve blocks in altmap. >> + */ >> + return IS_ALIGNED(vmemmap_size, PAGE_SIZE); > > Can we move that check into common code as well? > > If our (original) vmemmap size would not fit into a single page, we would be in trouble on any architecture. Did not check if it would be an issue for arm64 as well in case we would allow eventually wasting memory. > For x86 and arm we already do IS_ALIGNED(vmemmap_size, PMD_SIZE); in arch_supports_memmap_on_memory(). That should imply PAGE_SIZE alignment. If arm64 allow the usage of altmap.reserve, I would expect the arch_supports_memmap_on_memory to have the PAGE_SIZE check. Adding the PAGE_SIZE check in mhp_supports_memmap_on_memory() makes it redundant check for x86 and arm currently? modified mm/memory_hotplug.c @@ -1293,6 +1293,13 @@ static bool mhp_supports_memmap_on_memory(unsigned long size) */ if (!mhp_memmap_on_memory() || size != memory_block_size_bytes()) return false; + + /* + * Make sure the vmemmap allocation is fully contianed + * so that we always allocate vmemmap memory from altmap area. + */ + if (!IS_ALIGNED(vmemmap_size, PAGE_SIZE)) + return false; /* * Without page reservation remaining pages should be pageblock aligned. */
On 11.07.23 17:40, Aneesh Kumar K V wrote: > On 7/11/23 8:56 PM, David Hildenbrand wrote: >> On 11.07.23 06:48, Aneesh Kumar K.V wrote: >>> Radix vmemmap mapping can map things correctly at the PMD level or PTE >>> level based on different device boundary checks. Hence we skip the >>> restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also >>> makes the feature widely useful because to use PMD_SIZE vmemmap area we >>> require a memory block size of 2GiB >>> >>> We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature >>> can work with a memory block size of 256MB. Using altmap.reserve feature >>> to align things correctly at pageblock granularity. We can end up >>> losing some pages in memory with this. For ex: with a 256MiB memory block >>> size, we require 4 pages to map vmemmap pages, In order to align things >>> correctly we end up adding a reserve of 28 pages. ie, for every 4096 >>> pages 28 pages get reserved. >>> >>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> >>> --- >>> arch/powerpc/Kconfig | 1 + >>> arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++ >>> .../platforms/pseries/hotplug-memory.c | 3 +- >>> mm/memory_hotplug.c | 2 ++ >>> 4 files changed, 33 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>> index 116d6add0bb0..f890907e5bbf 100644 >>> --- a/arch/powerpc/Kconfig >>> +++ b/arch/powerpc/Kconfig >>> @@ -157,6 +157,7 @@ config PPC >>> select ARCH_HAS_UBSAN_SANITIZE_ALL >>> select ARCH_HAVE_NMI_SAFE_CMPXCHG >>> select ARCH_KEEP_MEMBLOCK >>> + select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU >>> select ARCH_MIGHT_HAVE_PC_PARPORT >>> select ARCH_MIGHT_HAVE_PC_SERIO >>> select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX >>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h >>> index 68817ea7f994..8e6c92dde6ad 100644 >>> --- a/arch/powerpc/include/asm/pgtable.h >>> +++ b/arch/powerpc/include/asm/pgtable.h >>> @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x) >>> int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size); >>> bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start, >>> unsigned long page_size); >>> +/* >>> + * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details >>> + * some of the restrictions. We don't check for PMD_SIZE because our >>> + * vmemmap allocation code can fallback correctly. The pageblock >>> + * alignment requirement is met using altmap->reserve blocks. >>> + */ >>> +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory >>> +static inline bool arch_supports_memmap_on_memory(unsigned long size) >>> +{ >>> + unsigned long nr_pages = size >> PAGE_SHIFT; >>> + unsigned long vmemmap_size = nr_pages * sizeof(struct page); >>> + >>> + if (!radix_enabled()) >>> + return false; >>> + >>> +#ifdef CONFIG_PPC_4K_PAGES >>> + return IS_ALIGNED(vmemmap_size, PMD_SIZE); >>> +#else >>> + /* >>> + * Make sure the vmemmap allocation is fully contianed >>> + * so that we always allocate vmemmap memory from altmap area. >>> + * The pageblock alignment requirement is met by using >>> + * reserve blocks in altmap. >>> + */ >>> + return IS_ALIGNED(vmemmap_size, PAGE_SIZE); >> >> Can we move that check into common code as well? >> >> If our (original) vmemmap size would not fit into a single page, we would be in trouble on any architecture. Did not check if it would be an issue for arm64 as well in case we would allow eventually wasting memory. >> > > > For x86 and arm we already do IS_ALIGNED(vmemmap_size, PMD_SIZE); in arch_supports_memmap_on_memory(). That should imply PAGE_SIZE alignment. > If arm64 allow the usage of altmap.reserve, I would expect the arch_supports_memmap_on_memory to have the PAGE_SIZE check. > > Adding the PAGE_SIZE check in mhp_supports_memmap_on_memory() makes it redundant check for x86 and arm currently? IMHO not an issue. The common code check is a bit weaker and the arch check a bit stronger. > > modified mm/memory_hotplug.c > @@ -1293,6 +1293,13 @@ static bool mhp_supports_memmap_on_memory(unsigned long size) > */ > if (!mhp_memmap_on_memory() || size != memory_block_size_bytes()) > return false; > + > + /* > + * Make sure the vmemmap allocation is fully contianed s/contianed/contained/ > + * so that we always allocate vmemmap memory from altmap area. In theory, it's not only the vmemmap size, but also the vmemmap start (that it doesn't start somewhere in between a page, crossing a page). I suspect the start is always guaranteed to be aligned (of the vmemmap size is aligned), correct? > + */ > + if (!IS_ALIGNED(vmemmap_size, PAGE_SIZE)) > + return false; > /* > * Without page reservation remaining pages should be pageblock aligned. > */ > >
On 7/11/23 9:14 PM, David Hildenbrand wrote: > On 11.07.23 17:40, Aneesh Kumar K V wrote: >> On 7/11/23 8:56 PM, David Hildenbrand wrote: >>> On 11.07.23 06:48, Aneesh Kumar K.V wrote: >>>> Radix vmemmap mapping can map things correctly at the PMD level or PTE >>>> level based on different device boundary checks. Hence we skip the >>>> restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also >>>> makes the feature widely useful because to use PMD_SIZE vmemmap area we >>>> require a memory block size of 2GiB >>>> >>>> We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature >>>> can work with a memory block size of 256MB. Using altmap.reserve feature >>>> to align things correctly at pageblock granularity. We can end up >>>> losing some pages in memory with this. For ex: with a 256MiB memory block >>>> size, we require 4 pages to map vmemmap pages, In order to align things >>>> correctly we end up adding a reserve of 28 pages. ie, for every 4096 >>>> pages 28 pages get reserved. >>>> >>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> >>>> --- >>>> arch/powerpc/Kconfig | 1 + >>>> arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++ >>>> .../platforms/pseries/hotplug-memory.c | 3 +- >>>> mm/memory_hotplug.c | 2 ++ >>>> 4 files changed, 33 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>>> index 116d6add0bb0..f890907e5bbf 100644 >>>> --- a/arch/powerpc/Kconfig >>>> +++ b/arch/powerpc/Kconfig >>>> @@ -157,6 +157,7 @@ config PPC >>>> select ARCH_HAS_UBSAN_SANITIZE_ALL >>>> select ARCH_HAVE_NMI_SAFE_CMPXCHG >>>> select ARCH_KEEP_MEMBLOCK >>>> + select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU >>>> select ARCH_MIGHT_HAVE_PC_PARPORT >>>> select ARCH_MIGHT_HAVE_PC_SERIO >>>> select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX >>>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h >>>> index 68817ea7f994..8e6c92dde6ad 100644 >>>> --- a/arch/powerpc/include/asm/pgtable.h >>>> +++ b/arch/powerpc/include/asm/pgtable.h >>>> @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x) >>>> int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size); >>>> bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start, >>>> unsigned long page_size); >>>> +/* >>>> + * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details >>>> + * some of the restrictions. We don't check for PMD_SIZE because our >>>> + * vmemmap allocation code can fallback correctly. The pageblock >>>> + * alignment requirement is met using altmap->reserve blocks. >>>> + */ >>>> +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory >>>> +static inline bool arch_supports_memmap_on_memory(unsigned long size) >>>> +{ >>>> + unsigned long nr_pages = size >> PAGE_SHIFT; >>>> + unsigned long vmemmap_size = nr_pages * sizeof(struct page); >>>> + >>>> + if (!radix_enabled()) >>>> + return false; >>>> + >>>> +#ifdef CONFIG_PPC_4K_PAGES >>>> + return IS_ALIGNED(vmemmap_size, PMD_SIZE); >>>> +#else >>>> + /* >>>> + * Make sure the vmemmap allocation is fully contianed >>>> + * so that we always allocate vmemmap memory from altmap area. >>>> + * The pageblock alignment requirement is met by using >>>> + * reserve blocks in altmap. >>>> + */ >>>> + return IS_ALIGNED(vmemmap_size, PAGE_SIZE); >>> >>> Can we move that check into common code as well? >>> >>> If our (original) vmemmap size would not fit into a single page, we would be in trouble on any architecture. Did not check if it would be an issue for arm64 as well in case we would allow eventually wasting memory. >>> >> >> >> For x86 and arm we already do IS_ALIGNED(vmemmap_size, PMD_SIZE); in arch_supports_memmap_on_memory(). That should imply PAGE_SIZE alignment. >> If arm64 allow the usage of altmap.reserve, I would expect the arch_supports_memmap_on_memory to have the PAGE_SIZE check. >> >> Adding the PAGE_SIZE check in mhp_supports_memmap_on_memory() makes it redundant check for x86 and arm currently? > > IMHO not an issue. The common code check is a bit weaker and the arch check a bit stronger. > >> ok will update >> modified mm/memory_hotplug.c >> @@ -1293,6 +1293,13 @@ static bool mhp_supports_memmap_on_memory(unsigned long size) >> */ >> if (!mhp_memmap_on_memory() || size != memory_block_size_bytes()) >> return false; >> + >> + /* >> + * Make sure the vmemmap allocation is fully contianed > > s/contianed/contained/ > >> + * so that we always allocate vmemmap memory from altmap area. > > In theory, it's not only the vmemmap size, but also the vmemmap start (that it doesn't start somewhere in between a page, crossing a page). I suspect the start is always guaranteed to be aligned (of the vmemmap size is aligned), correct? > That is correct. >> + */ >> + if (!IS_ALIGNED(vmemmap_size, PAGE_SIZE)) >> + return false; >> /* >> * Without page reservation remaining pages should be pageblock aligned. >> */ >> -aneesh >
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 116d6add0bb0..f890907e5bbf 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -157,6 +157,7 @@ config PPC select ARCH_HAS_UBSAN_SANITIZE_ALL select ARCH_HAVE_NMI_SAFE_CMPXCHG select ARCH_KEEP_MEMBLOCK + select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU select ARCH_MIGHT_HAVE_PC_PARPORT select ARCH_MIGHT_HAVE_PC_SERIO select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 68817ea7f994..8e6c92dde6ad 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x) int __meminit vmemmap_populated(unsigned long vmemmap_addr, int vmemmap_map_size); bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start, unsigned long page_size); +/* + * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details + * some of the restrictions. We don't check for PMD_SIZE because our + * vmemmap allocation code can fallback correctly. The pageblock + * alignment requirement is met using altmap->reserve blocks. + */ +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory +static inline bool arch_supports_memmap_on_memory(unsigned long size) +{ + unsigned long nr_pages = size >> PAGE_SHIFT; + unsigned long vmemmap_size = nr_pages * sizeof(struct page); + + if (!radix_enabled()) + return false; + +#ifdef CONFIG_PPC_4K_PAGES + return IS_ALIGNED(vmemmap_size, PMD_SIZE); +#else + /* + * Make sure the vmemmap allocation is fully contianed + * so that we always allocate vmemmap memory from altmap area. + * The pageblock alignment requirement is met by using + * reserve blocks in altmap. + */ + return IS_ALIGNED(vmemmap_size, PAGE_SIZE); +#endif +} + #endif /* CONFIG_PPC64 */ #endif /* __ASSEMBLY__ */ diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index 9c62c2c3b3d0..1447509357a7 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -617,6 +617,7 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index) static int dlpar_add_lmb(struct drmem_lmb *lmb) { + mhp_t mhp_flags = MHP_NONE | MHP_MEMMAP_ON_MEMORY; unsigned long block_sz; int nid, rc; @@ -637,7 +638,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb) nid = first_online_node; /* Add the memory */ - rc = __add_memory(nid, lmb->base_addr, block_sz, MHP_NONE); + rc = __add_memory(nid, lmb->base_addr, block_sz, mhp_flags); if (rc) { invalidate_lmb_associativity_index(lmb); return rc; diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index f36aec1f7626..0c4d3fdd31a2 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -2108,6 +2108,8 @@ static int __ref try_remove_memory(u64 start, u64 size) * right thing if we used vmem_altmap when hot-adding * the range. */ + mhp_altmap.base_pfn = PHYS_PFN(start); + mhp_altmap.free = PHYS_PFN(size) - nr_vmemmap_pages; mhp_altmap.alloc = nr_vmemmap_pages; altmap = &mhp_altmap; }
Radix vmemmap mapping can map things correctly at the PMD level or PTE level based on different device boundary checks. Hence we skip the restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also makes the feature widely useful because to use PMD_SIZE vmemmap area we require a memory block size of 2GiB We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature can work with a memory block size of 256MB. Using altmap.reserve feature to align things correctly at pageblock granularity. We can end up losing some pages in memory with this. For ex: with a 256MiB memory block size, we require 4 pages to map vmemmap pages, In order to align things correctly we end up adding a reserve of 28 pages. ie, for every 4096 pages 28 pages get reserved. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++ .../platforms/pseries/hotplug-memory.c | 3 +- mm/memory_hotplug.c | 2 ++ 4 files changed, 33 insertions(+), 1 deletion(-)