Re: [PATCH RFC 20/37] mm: compaction: Reserve metadata storage in compaction_alloc()

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Peter,

On Mon, Nov 20, 2023 at 08:49:32PM -0800, Peter Collingbourne wrote:
> Hi Alexandru,
> 
> On Wed, Aug 23, 2023 at 6:16 AM Alexandru Elisei
> <alexandru.elisei@arm.com> wrote:
> >
> > If the source page being migrated has metadata associated with it, make
> > sure to reserve the metadata storage when choosing a suitable destination
> > page from the free list.
> >
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> > ---
> >  mm/compaction.c | 9 +++++++++
> >  mm/internal.h   | 1 +
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index cc0139fa0cb0..af2ee3085623 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -570,6 +570,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> >         bool locked = false;
> >         unsigned long blockpfn = *start_pfn;
> >         unsigned int order;
> > +       int ret;
> >
> >         /* Strict mode is for isolation, speed is secondary */
> >         if (strict)
> > @@ -626,6 +627,11 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> >
> >                 /* Found a free page, will break it into order-0 pages */
> >                 order = buddy_order(page);
> > +               if (metadata_storage_enabled() && cc->reserve_metadata) {
> > +                       ret = reserve_metadata_storage(page, order, cc->gfp_mask);
> 
> At this point the zone lock is held and preemption is disabled, which
> makes it invalid to call reserve_metadata_storage.

You are correct, I missed that. I dropped reserving tag storage during
compaction in the next iteration, so fortunately I unintentionally fixed
it.

Thanks,
Alex

> 
> Peter
> 
> > +                       if (ret)
> > +                               goto isolate_fail;
> > +               }
> >                 isolated = __isolate_free_page(page, order);
> >                 if (!isolated)
> >                         break;
> > @@ -1757,6 +1763,9 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
> >         struct compact_control *cc = (struct compact_control *)data;
> >         struct folio *dst;
> >
> > +       if (metadata_storage_enabled())
> > +               cc->reserve_metadata = folio_has_metadata(src);
> > +
> >         if (list_empty(&cc->freepages)) {
> >                 isolate_freepages(cc);
> >
> > diff --git a/mm/internal.h b/mm/internal.h
> > index d28ac0085f61..046cc264bfbe 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -492,6 +492,7 @@ struct compact_control {
> >                                          */
> >         bool alloc_contig;              /* alloc_contig_range allocation */
> >         bool source_has_metadata;       /* source pages have associated metadata */
> > +       bool reserve_metadata;
> >  };
> >
> >  /*
> > --
> > 2.41.0
> >