Re: [PATCH] mm: avoid use of BIT() macro for initialising VMA flags

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Dec 05, 2025 at 05:50:37PM +0000, Lorenzo Stoakes wrote:
> Commit 2b6a3f061f11 ("mm: declare VMA flags by bit") significantly changed
> how VMA flags are declared, utilising an enum of VMA bit values and
> ifdef-fery VM_xxx flag declarations via macro.
> 
> As part of this change, it uses INIT_VM_FLAG() to define VM_xxx flags from
> the newly introduced VMA bit numbers.
> 
> However, use of this macro results in apparently unfortunate macro
> expansion and resulted in a performance degradation.This appears to be due
> to the (__force int), which is required for the sparse typechecking to
> work.

> -#define INIT_VM_FLAG(name) BIT((__force int) VMA_ ## name ## _BIT)
> +#define INIT_VM_FLAG(name) (1UL << (__force int)(VMA_ ## name ## _BIT))

What the hell is __bitwise doing on these enum values?
Could we please get rid of that ridiculous cargo-culting?

Bitwise operations on BIT NUMBERS make no sense whatsoever; why are those
declared __bitwise?