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Explain that vm_page_array is mapped to describe the memory, not the

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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
This commit is contained in:
Konstantin Belousov 2015-04-08 19:46:13 +00:00
parent ea1401b9a9
commit a7496c776d
1 changed files with 8 additions and 3 deletions
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11
sys/i386/include/pmap.h
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@ -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