On Wed, 28 Mar 2018 08:51:42 +0800 Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
> On Tue, Mar 27, 2018 at 03:47:40PM -0700, Andrew Morton wrote:
> >On Tue, 27 Mar 2018 11:57:07 +0800 Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
> >
> >> find_min_pfn_for_node() iterate on pfn range to find the minimum pfn for a
> >> node. The memblock_region in memblock_type are already ordered, which means
> >> the first hit in iteration is the minimum pfn.
> >>
> >> This patch returns the fist hit instead of iterating the whole regions.
> >>
> >> ...
> >>
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -6365,14 +6365,14 @@ unsigned long __init node_map_pfn_alignment(void)
> >> /* Find the lowest pfn for a node */
> >> static unsigned long __init find_min_pfn_for_node(int nid)
> >> {
> >> - unsigned long min_pfn = ULONG_MAX;
> >> - unsigned long start_pfn;
> >> + unsigned long min_pfn;
> >> int i;
> >>
> >> - for_each_mem_pfn_range(i, nid, &start_pfn, NULL, NULL)
> >> - min_pfn = min(min_pfn, start_pfn);
> >> + for_each_mem_pfn_range(i, nid, &min_pfn, NULL, NULL) {
> >> + break;
> >> + }
> >
> >That would be the weirdest-looking code snippet in mm/!
> >
>
> You mean the only break in a for_each loop? Hmm..., this is really not that
> nice. Haven't noticed could get a "best" in this way :-)
I guess we can make it nicer by adding a comment along the lines of
/*
* Use for_each_mem_pfn_range() to locate the lowest valid pfn in the
* range. We only need to iterate a single time, as the pfn's are
* sorted in ascending order.
*/
Because adding a call to the obviously-internal __next_mem_pfn_range()
isn't very nice either.
Anyway, please have a think, see what we can come up with.
