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| author | kib <kib@FreeBSD.org> | 2015-04-08 19:46:13 +0000 |
|---|---|---|
| committer | kib <kib@FreeBSD.org> | 2015-04-08 19:46:13 +0000 |
| commit | 006ec965299dcd8d9be11a465e511393bebdea37 (patch) | |
| tree | 08f0bd3dc32be0f8804184d00b9397c36392f1ca /sys/i386/include/pmap.h | |
| parent | f57a64395c7d842a3db1091751a43be732c84af2 (diff) | |
| download | FreeBSD-src-006ec965299dcd8d9be11a465e511393bebdea37.zip FreeBSD-src-006ec965299dcd8d9be11a465e511393bebdea37.tar.gz | |
Explain that vm_page_array is mapped to describe the memory, not the
memory itself. Provide the formula to calculate the number of
required page tables. Correct the size of the struct vm_page for
non-PAE case.
Reviewed by: alc, jhb (previous version)
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Diffstat (limited to 'sys/i386/include/pmap.h')
| -rw-r--r-- | sys/i386/include/pmap.h | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/sys/i386/include/pmap.h b/sys/i386/include/pmap.h index 05656cd..2c9a409 100644 --- a/sys/i386/include/pmap.h +++ b/sys/i386/include/pmap.h @@ -122,13 +122,18 @@ */ #define VADDR(pdi, pti) ((vm_offset_t)(((pdi)<<PDRSHIFT)|((pti)<<PAGE_SHIFT))) -/* Initial number of kernel page tables. */ +/* + * The initial number of kernel page table pages that are constructed + * by locore must be sufficient to map vm_page_array. That number can + * be calculated as follows: + * max_phys / PAGE_SIZE * sizeof(struct vm_page) / NBPDR + * PAE: max_phys 16G, sizeof(vm_page) 76, NBPDR 2M, 152 page table pages. + * Non-PAE: max_phys 4G, sizeof(vm_page) 68, NBPDR 4M, 18 page table pages. + */ #ifndef NKPT #ifdef PAE -/* 152 page tables needed to map 16G (76B "struct vm_page", 2M page tables). */ #define NKPT 240 #else -/* 18 page tables needed to map 4G (72B "struct vm_page", 4M page tables). */ #define NKPT 30 #endif #endif |
