On Tue, Jul 14, 2020 at 02:12:03PM -0700, Mike Kravetz wrote: >On 7/14/20 3:02 AM, Vlastimil Babka wrote: >> On 7/14/20 11:57 AM, Wei Yang wrote: >>> On Tue, Jul 14, 2020 at 11:22:03AM +0200, Vlastimil Babka wrote: >>>> On 7/14/20 11:13 AM, Vlastimil Babka wrote: >>>>> On 7/14/20 9:34 AM, Wei Yang wrote: >>>>>> The second parameter of for_each_node_mask_to_[alloc|free] is a loop >>>>>> variant, which is not used outside of loop iteration. >>>>>> >>>>>> Let's hide this. >>>>>> >>>>>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> >>>>>> --- >>>>>> mm/hugetlb.c | 38 ++++++++++++++++++++------------------ >>>>>> 1 file changed, 20 insertions(+), 18 deletions(-) >>>>>> >>>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>>> index 57ece74e3aae..9c3d15fb317e 100644 >>>>>> --- a/mm/hugetlb.c >>>>>> +++ b/mm/hugetlb.c >>>>>> @@ -1196,17 +1196,19 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed) >>>>>> return nid; >>>>>> } >>>>>> >>>>>> -#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask) \ >>>>>> - for (nr_nodes = nodes_weight(*mask); \ >>>>>> - nr_nodes > 0 && \ >>>>>> +#define for_each_node_mask_to_alloc(hs, node, mask) \ >>>>>> + int __nr_nodes; \ >>>>>> + for (__nr_nodes = nodes_weight(*mask); \ >>>>> >>>>> The problem with this is that if I use the macro twice in the same block, this >>>>> will redefine __nr_nodes and fail to compile, no? >>>>> In that case it's better to avoid setting up this trap, IMHO. >>>> >>>> Ah, and it will also generate the following warning, if the use of for_each* >>>> macro is not the first thing after variable declarations, but there's another >>>> statement before: >>>> >>>> warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement] >>>> >>>> Instead we should switch to C99 and declare it as "for (int __nr_nodes" :P >>> >>> Hmm... I tried what you suggested, but compiler complains. >>> >>> 'for' loop initial declarations are only allowed in C99 or C11 mode >> >> Yes, by "we should switch to C99" I meant that the kernel kbuild system would >> need to switch. Not a trivial change... >> Without that, I don't see how your patch is possible to do safely. > >Vlastimil, thanks for pointing out future potential issues with this patch. >I likely would have missed that. > >Wei, thanks for taking the time to put together the patch. However, I tend >to agree with Vlastimil's assesment. The cleanup is not worth the risk of >running into issues if someone uses multiple instances of the macro. Yep, thanks all for your feedback. >-- >Mike Kravetz -- Wei Yang Help you, Help me
