mm: replace recently unstable bitmap_len()

[Zildj1an]

The usage of the unstable library feature 'int_roundings' would trigger a compilation error (See Rust issue #88581). Replace it with a standard integer division.

This is the error:

error[E0658]: use of unstable library feature 'int_roundings'
   --> src/mm/validate.rs:151:19
    |
151 |         num_pages.div_ceil(u64::BITS as usize)
    |                   ^^^^^^^^
    |
    = note: see issue #88581 <https://github.com/rust-lang/rust/issues/88581> for more information

Fixes: 2b0162d (mm/validate: migrate all pages in bitmap)

[00xc]

div_ceil should be stable since Rust 1.73. Have you updated your toolchain?

[Zildj1an]

div_ceil should be stable since Rust 1.73. Have you updated your toolchain?

You're absolutely correct! Doing rustup update solved it. I have removed the Fixes tag and updated the commit message; even though this works for latest toolchains I think we should still apply this change, given that we don't really need this (recently unstable) utility to perform the operation at hand.

[stefano-garzarella]

Not a strong opinion, but eventually we can avoid additional_u64 and do something like this:

Suggested change

	let additional_u64 = if self.region.len() % PAGE_SIZE != 0 {
	1
	} else {
	0
	};
	num_pages + additional_u64
	if self.region.len() % PAGE_SIZE != 0 {
	num_pages + 1
	} else {
	num_pages
	}

[joergroedel]

I think we can leave the code as-is, Rust 1.73 is from October so we can expect developers to update.