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SubjectRe: [PATCH] mm: be more verbose for alloc_contig_range faliures
Date
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.

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.

> + }
> putback_movable_pages(&cc->migratepages);
> return ret;
> }
> @@ -8728,6 +8737,8 @@ struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
> pfn = ALIGN(zone->zone_start_pfn, nr_pages);
> while (zone_spans_last_pfn(zone, pfn, nr_pages)) {
> if (pfn_range_valid_contig(zone, pfn, nr_pages)) {
> + unsigned long gfp_flags;
> +
> /*
> * We release the zone lock here because
> * alloc_contig_range() will also lock the zone
> @@ -8736,8 +8747,11 @@ struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
> * and cause alloc_contig_range() to fail...
> */
> spin_unlock_irqrestore(&zone->lock, flags);
> +
> + if (zone_idx(zone) != ZONE_MOVABLE)
> + gfp_flags = gfp_mask | __GFP_NOWARN;

This feels wrong. It might be better to make that decision inside
__alloc_contig_migrate_range() based on cc->zone.

--
Thanks,

David / dhildenb

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