Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH] mm: be more verbose for alloc_contig_range faliures | Date | Wed, 17 Feb 2021 18:34:13 +0100 |
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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@kernel.org> >>> --- >>> 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
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