On Thu, Dec 03, 2020 at 11:23:10PM +0800, [email protected] wrote: > From: Hailong Liu <[email protected]> > > 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 <[email protected]> > --- > 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.
