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

[Peter Collingbourne]

Hi Alexandru,

On Wed, Aug 23, 2023 at 6:16 AM Alexandru Elisei
<alexandru.elisei@xxxxxxx> 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@xxxxxxx>
> ---
>  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.

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
>