Anshuman Khandual <khand...@linux.vnet.ibm.com> writes: > Add some explaination to the layout of vmemmap virtual address > space and how physical page mapping is only used for valid PFNs > present at any point on the system. >
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> > Signed-off-by: Anshuman Khandual <khand...@linux.vnet.ibm.com> > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 41 > ++++++++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 8d1c41d..9db4a86 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -26,6 +26,47 @@ > #define IOREMAP_BASE (PHB_IO_END) > #define IOREMAP_END (KERN_VIRT_START + KERN_VIRT_SIZE) > > +/* > + * Starting address of the virtual address space where all page structs > + * for the system physical memory are stored under the vmemmap sparse > + * memory model. All possible struct pages are logically stored in a > + * sequence in this virtual address space irrespective of the fact > + * whether any given PFN is valid or even the memory section is valid > + * or not. During boot and memory hotplug add operation when new memory > + * sections are added, real physical allocation and hash table bolting > + * will be performed. This saves precious physical memory when the system > + * really does not have valid PFNs in some address ranges. > + * > + * vmemmap +--------------+ > + * + | page struct +----------+ PFN is valid > + * | +--------------+ | > + * | | page struct | | PFN is invalid > + * | +--------------+ | > + * | | page struct +------+ | > + * | +--------------+ | | > + * | | page struct | | | > + * | +--------------+ | | > + * | | page struct | | | > + * | +--------------+ | | > + * | | page struct +--+ | | > + * | +--------------+ | | | > + * | | page struct | | | | +-------------+ > + * | +--------------+ | | +-----> | PFN | > + * | | page struct | | | +-------------+ > + * | +--------------+ | +---------> | PFN | > + * | | page struct | | +-------------+ > + * | +--------------+ +-------------> | PFN | > + * | | page struct | +-------------+ > + * | +--------------+ +----> | PFN | > + * | | page struct | | +-------------+ > + * | +--------------+ | Bolted in hash table > + * | | page struct +-----------+ > + * v +--------------+ > + * > + * VMEMMAP_BASE (0xf000000000000000) region has a total range of 64TB but > + * then it uses NR_MEM_SECTIONS * PAGES_PER_SECTION * sizeof(page struct) > + * amount of virtual memory from it. > + */ > #define vmemmap ((struct page *)VMEMMAP_BASE) > > /* Advertise special mapping type for AGP */ > -- > 2.1.0 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev