On Tue, Feb 09, 2021 at 07:17:59PM +0100, David Hildenbrand wrote: > On 09.02.21 18:50, Minchan Kim wrote: > > __alloc_contig_migrate_range already has lru_add_drain_all call > > via migrate_prep. It's necessary to move LRU taget pages into > > LRU list to be able to isolated. However, lru_add_drain_all call > > after __alloc_contig_migrate_range is called is pointless. > > > > This patch removes it. > > > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > --- > > mm/page_alloc.c | 2 -- > > 1 file changed, 2 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 6446778cbc6b..f8fbee73dd6d 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -8603,8 +8603,6 @@ int alloc_contig_range(unsigned long start, unsigned long end, > > * isolated thus they won't get removed from buddy. > > */ > > - lru_add_drain_all(); > > - > > order = 0; > > outer_start = start; > > while (!PageBuddy(pfn_to_page(outer_start))) { > > > > I was expecting some magical reason why this is still required but I am not > able to find a compelling one. Maybe this is really some historical > artifact. > > Let's see if other people know why this call here still exists. I also stumbled upon this while working on adding hugetlb support for alloc_acontig_range [1]. I have to confess I puzzled me a bit. I saw it going back to when the function was first introduced by commit 041d3a8cdc18dc375a128d90bbb753949a81b1fb Author: Michal Nazarewicz <mina86@xxxxxxxxxx> Date: Thu Dec 29 13:09:50 2011 +0100 mm: page_alloc: introduce alloc_contig_range() It does not make much sense to me. At this point our pages are free, so we do not care about LRU handling here. But I might be missing something. [1] https://lore.kernel.org/linux-mm/20210208103935.GA32103@linux/T/#md651fc6e73c656105179382f92f8b2d6073051d1 -- Oscar Salvador SUSE L3