On 17.02.21 18:26, Minchan Kim wrote:
On Wed, Feb 17, 2021 at 05:51:27PM +0100, David Hildenbrand wrote:
On 17.02.21 17:36, Minchan Kim wrote:
alloc_contig_range is usually used on cma area or movable zone.
It's critical if the page migration fails on those areas so
dump more debugging message like memory_hotplug unless user
specifiy __GFP_NOWARN.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
mm/page_alloc.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0b55c9c95364..67f3ee3a1528 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8486,6 +8486,15 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
NULL, (unsigned long)&mtc, cc->mode, MR_CONTIG_RANGE);
}
if (ret < 0) {
+ if (!(cc->gfp_mask & __GFP_NOWARN)) {
+ struct page *page;
+
+ list_for_each_entry(page, &cc->migratepages, lru) {
+ pr_warn("migrating pfn %lx failed ret:%d ",
+ page_to_pfn(page), ret);
+ dump_page(page, "migration failure");
+ }
This can create *a lot* of noise. For example, until huge pages are actually
considered, we will choke on each end every huge page - and might do so over
and over again.
I am not familiar with huge page status at this moment but why couldn't
they use __GFP_NOWARN if they are supposed to fail frequently?
any alloc_contig_range() user will fail on hugetlbfs pages right now
when they are placed into CMA/ZONE_MOVABLE. Oscar is working on that
upstream.
This might be helpful for debugging, but is unacceptable for production
systems for now I think. Maybe for now, do it based on CONFIG_DEBUG_VM.
If it's due to huge page you mentioned above and caller passes
__GFP_NOWARN in that case, couldn't we enable always-on?
It would make sense to add that for virito-mem when calling
alloc_contig_range(). For now I didn't do so, because there were not
that many messages yet - alloc_contig_range() essentially didn't
understand __GFP_NOWARN.
We should then also stop printing the "PFNs busy ..." part from
alloc_contig_range() with __GFP_NOWARN.
Actually, I am targeting cma allocation failure, which should
be rather rare compared to other call sites but critical to fail.
If it's concern to emit too many warning message, I will scope
down for site for only cma allocation.
If you add "__GFP_NOWARN" when !ZONE_MOVABLE, how would you ever print
something for CMA? What am I missing? CMA is usually not on ZONE_MOVABLE.
--
Thanks,
David / dhildenb
