Home/ Questions/Q 7947165
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-04T01:21:16+00:00

On 32bit x86 platform, if vmalloc() can allocate memory from either ZONE_NORMAL or ZONE_HIGHMEM,

  • 0

On 32bit x86 platform, if vmalloc() can allocate memory from either ZONE_NORMAL or ZONE_HIGHMEM, does it mean that even if I enlarge ZONE_HIGHMEM, the actual total range that vmalloc() can use is unchanged? I did a test to enlarge ZONE_HIGHMEM, the one time allocation of vmalloc() can be much bigger than before. So does it mean that vmalloc() actually allocate memory from ZONE_HIGHMEM only?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    vmalloc prefers ZONE_HIGHMEM, if it exists, but can fall back to ZONE_NORMAL.

    However, in a machine with 1GB or more (i.e. any modern machine), vmalloc is limited by virtual memory (the vmalloc region), not by physical memory.
    In such a case, the vmalloc region is 128MB (unless enlarged by vmalloc_reserve), while ZONE_HIGHMEM is that plus all memory above 1GB – normally much larger.

    What you enlarge is actually the vmalloc virtual memory region, and enlarging it lets you vmalloc more. This indirectly enlarges ZONE_HIGHMEM, but this isn’t very impotrant.

    • 0