On Fri, Jul 26, 2019 at 5:36 PM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
>
> On 25/07/2019 20.42, Pengfei Li wrote:
> > Because "order" will never be negative in __rmqueue_fallback(),
> > so just make "order" unsigned int.
> > And modify trace_mm_page_alloc_extfrag() accordingly.
> >
>
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 75c18f4fd66a..1432cbcd87cd 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2631,8 +2631,8 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> > * condition simpler.
> > */
> > static __always_inline bool
> > -__rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
> > - unsigned int alloc_flags)
> > +__rmqueue_fallback(struct zone *zone, unsigned int order,
> > + int start_migratetype, unsigned int alloc_flags)
> > {
>
> Please read the last paragraph of the comment above this function, run
> git blame to figure out when that was introduced, and then read the full
> commit description.
Thanks for your comments.
I have read the commit info of commit b002529d2563 ("mm/page_alloc.c:
eliminate unsigned confusion in __rmqueue_fallback").
And I looked at the discussion at https://lkml.org/lkml/2017/6/21/684 in detail.
> Here be dragons. At the very least, this patch is
> wrong in that it makes that comment inaccurate.
I wonder if you noticed the commit 6bb154504f8b ("mm, page_alloc: spread
allocations across zones before introducing fragmentation").
Commit 6bb154504f8b introduces a local variable min_order in
__rmqueue_fallback().
And you can see
for (current_order = MAX_ORDER - 1; current_order >= min_order;
--current_order) {
The “current_order” and "min_order" are int, so here is ok.
Since __rmqueue_fallback() is only called by __rmqueue() and "order" is unsigned
int in __rmqueue(), then I think that making "order" is also unsigned
int is good.
Maybe I should also modify the comments here?
>
> Rasmus
Thank you again for your review.
--
Pengfei
