On Thu 20-12-18 15:21:27, Oscar Salvador wrote: > On Thu, Dec 20, 2018 at 02:41:32PM +0100, Oscar Salvador wrote: > > On Thu, Dec 20, 2018 at 02:06:06PM +0100, Michal Hocko wrote: > > > You did want iter += skip_pages - 1 here right? > > > > Bleh, yeah. > > I am taking vacation today so my brain has left me hours ago, sorry. > > Should be: > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 4812287e56a0..0634fbdef078 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -8094,7 +8094,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, > > goto unmovable; > > > > skip_pages = (1 << compound_order(head)) - (page - head); > > - iter = round_up(iter + 1, skip_pages) - 1; > > + iter += skip_pages - 1; > > continue; > > } > > On a second thought, I think it should not really matter. > > AFAICS, we can have these scenarios: > > 1) the head page is the first page in the pabeblock > 2) first page in the pageblock is not a head but part of a hugepage > 3) the head is somewhere within the pageblock > > For cases 1) and 3), iter will just get the right value and we will > break the loop afterwards. > > In case 2), iter will be set to a value to skip over the remaining pages. > > I am assuming that hugepages are allocated and packed together. > > Note that I am not against the change, but I just wanted to see if there is > something I am missing. Yes, you are missing that this code should be as sane as possible ;) You are right that we are only processing one pageorder worth of pfns and that the page order is bound to HUGETLB_PAGE_ORDER _right_now_. But there is absolutely zero reason to hardcode that assumption into a simple loop, right? -- Michal Hocko SUSE Labs
