Re: [PATCH 4/4] mm: align file-backed mmap to exec folio order in thp_get_unmapped_area

[WANG Rui]

> +	if (exec_folio_order()) {
> +		unsigned long folio_size = PAGE_SIZE << exec_folio_order();
> +
> +		ret = __thp_get_unmapped_area(filp, addr, len, off, flags,
> +					      folio_size, vm_flags);
> +		if (ret)
> +			return ret;
> +	}
> +

I noticed that even when the code segment of a user-space shared library
satisfies PMD_SIZE (32MB), it still doesn’t end up at a PMD-aligned virtual
address. This might be the fallback you mentioned. Adjusting p_align in the
ld.so ELF loader does work, though it also avoids extremely large PMD_SIZE
values (capped at ≤32M).

It would probably be better to skip the PMD_SIZE == folio_sz case here,
so we don’t end up calling __thp_get_unmapped_area() twice with the same
parameters.

Thanks,
Rui