Chapter3:MemoryManagement
Table 3-6: Different Splitting Ratios for the IA-32 Virtual Address Space, and the
Resulting Maximum Identity-Mapped Physical Memory.
Ratio CONFIG_PAGE_OFFSET MAXMEM(MiB)
3:1 0xC0000000 896
≈3:1 0xB0000000 1152
2:2 0x80000000 1920
≈2:2 0x78000000 2048
1:3 0x40000000 2944
PAE enabled?
Use PSE, PGE extensions if possible
Initialize fixmaps
paging_init
set_nx
pagetable_init
kernel_physical_mapping_init
permanent_kmaps_init
load_cr3
__flush_all_tlb
kmap_init
Figure 3-16: Code flow diagram forpaging_init.
pagetable_initfirst initializes the page tables of the system usingswapper_pg_diras a basic (this
variable was previously used to hold the provisional data). Two extensions available on all modern
IA-32 variants are then enabled (only a few very old Pentium implementations do not support these).
❑ Support for large memory pages. The size of specially marked pages is 4 MiB instead of the usual
4 KiB. This option is used for kernel pages because they are never swapped out. Increasing the
page size means that fewer page table entries are needed, and this has a positive impact on the
translation lookaside buffers (TLBs), which are then less burdened with kernel data.
❑ If possible, kernel pages are provided with a further attribute (_PAGE_GLOBAL) that is why the
__PAGE_GLOBALbit is activated in the__PAGE_KERNELand__PAGE_KERNEL_EXECvariables. These
