On Thu, Dec 03, 2020 at 11:23:10PM +0800, carver4lio@xxxxxxx wrote:
> From: Hailong Liu <liu.hailong6@xxxxxxxxxx>
>
> When system in the booting stage, pages span from [start, end] of a memblock
> are freed to buddy in a order as large as possible (less than MAX_ORDER) at
> first, then decrease gradually to a proper order(less than end) in a loop.
>
> However, *min(MAX_ORDER - 1UL, __ffs(start))* can not get the largest order
> in some cases.
Do you have examples?
What is the memory configration that casues suboptimal order selection
and what is the order in this case?
> Instead, *__ffs(end - start)* may be more appropriate and meaningful.
As several people reported using __ffs(end - start) is not correct.
If the order selection is indeed suboptimal we'd need some better
formula ;-)
> Signed-off-by: Hailong Liu <liu.hailong6@xxxxxxxxxx>
> ---
> mm/memblock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index b68ee8678..7c6d0dde7 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1931,7 +1931,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
> int order;
>
> while (start < end) {
> - order = min(MAX_ORDER - 1UL, __ffs(start));
> + order = min(MAX_ORDER - 1UL, __ffs(end - start));
>
> while (start + (1UL << order) > end)
> order--;
> --
> 2.17.1
>
>
--
Sincerely yours,
Mike.
