On Wed, Feb 17, 2021 at 06:34:13PM +0100, David Hildenbrand wrote:
> 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.
Until then, how about adding this under !CONFIG_HUGETLBFS?
>
> >
> > >
> > > 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.
Yub.
>
> >
> > 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.
If the caller of cma_alloc passed __GFP_NOWARN, I don't care since
caller explictly declare it's not critical. What I'd like to catch up
is cma_alloc with !__GFP_NOWARN sites.
