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

Alexandru Elisei
2023-11-21T11:54:43Z

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
> >