static unsigned long _init setup_memory(void)
#ifdef CONFIG_HIGHMEM high_memory =
#else high_memory =
max_low_pfn specifies the number of memory pages present on systems with less than 896 MiB. The value is also limited upwards to the maximum number of pages that fit in 896 MiB (the exact calculation is given in find_max_low_pfn). If highmem support is enabled, high_memory indicates the bound between two memory areas, which is always at 896 MiB.
There is a gap with a minimum size of vmalloc_offset between the direct mapping of all RAM pages and the area for non-contiguous allocations.
Continue reading here: Includeasmx86pgtable32h
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