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SubjectRe: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit
On Thu, Jan 18, 2024 at 05:35:04AM -0800, Yang Shi wrote:
> It doesn't make too much sense to force huge page alignment on 32 bit
> system due to the constrained virtual address space.
>
> [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d

I feel sure there are shorter URLs for those messages ...

> @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
> loff_t off_align = round_up(off, size);
> unsigned long len_pad, ret;
>
> + /*
> + * It doesn't make too much sense to froce huge page alignment on
> + * 32 bit system or compat userspace due to the contrained virtual
> + * address space and address entropy.
> + */

I honestly wouldn't even comment this. But if you must,

/* Using THP alignment is not as important as address randomisation */

> + if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> + return 0;
> +
> if (off_end <= off_align || (off_end - off_align) < size)
> return 0;
>
> --
> 2.41.0
>

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