On Tue, Mar 27, 2018 at 06:37:57PM -0700, Andrew Morton wrote:
>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.
Yep, you are right.
>
>Anyway, please have a think, see what we can come up with.
My approach is to add a macro fist_mem_pfn() as a self-explain wrapper of
__next_mem_pfn_range().
Hope you would like this :-)
--
Wei Yang
Help you, Help me
