Question

From the file /vobs/linux/kernel/linux/arch/mips/kernel/setup.c (Linux 2.6.30)

    pr_info("Wasting %lu bytes for tracking %lu unused pages\n",
        (min_low_pfn - ARCH_PFN_OFFSET) * sizeof(struct page),
        min_low_pfn - ARCH_PFN_OFFSET);

This line prints

Wasting 64 bytes for tracking 2 unused pages

On my device during boot. What does it actually mean? Why are those bytes wasted?

Answer 1

There is an array of struct page structures, one for each page in physical lowmem.

This message is shown because the memory map provided by the bootloader has reserved the first two pages in your physical memory – those pages will never be used, but there’s still two corresponding struct page structures for them.

I wouldn’t worry about it, 64 bytes is pretty trivial.