Date: Wed, 8 Apr 2015 19:46:13 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r281272 - head/sys/i386/include Message-ID: <201504081946.t38JkD8f000594@svn.freebsd.org>
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Author: kib Date: Wed Apr 8 19:46:13 2015 New Revision: 281272 URL: https://svnweb.freebsd.org/changeset/base/281272 Log: 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 Modified: head/sys/i386/include/pmap.h Modified: head/sys/i386/include/pmap.h ============================================================================== --- head/sys/i386/include/pmap.h Wed Apr 8 19:12:38 2015 (r281271) +++ head/sys/i386/include/pmap.h Wed Apr 8 19:46:13 2015 (r281272) @@ -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
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