On Wed, Apr 30, 2014 at 05:45:27PM -0700, David Rientjes wrote:
> Memory compaction works by having a "freeing scanner" scan from one end of a
> zone which isolates pages as migration targets while another "migrating scanner"
> scans from the other end of the same zone which isolates pages for migration.
>
> When page migration fails for an isolated page, the target page is returned to
> the system rather than the freelist built by the freeing scanner. This may
> require the freeing scanner to continue scanning memory after suitable migration
> targets have already been returned to the system needlessly.
>
> This patch returns destination pages to the freeing scanner freelist when page
> migration fails. This prevents unnecessary work done by the freeing scanner but
> also encourages memory to be as compacted as possible at the end of the zone.
>
> Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/compaction.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -797,6 +797,19 @@ static struct page *compaction_alloc(struct page *migratepage,
> }
>
> /*
> + * This is a migrate-callback that "frees" freepages back to the isolated
> + * freelist. All pages on the freelist are from the same zone, so there is no
> + * special handling needed for NUMA.
> + */
> +static void compaction_free(struct page *page, unsigned long data)
> +{
> + struct compact_control *cc = (struct compact_control *)data;
> +
> + list_add(&page->lru, &cc->freepages);
> + cc->nr_freepages++;
With this change, migration_page() handles cc->nr_freepages consistently, so
we don't have to run over freelist to update this count in update_nr_listpages()?
I'm not sure if that's also true for cc->nr_migratepages, but if it is,
we can completely remove update_nr_listpages().
Thanks,
Naoya Horiguchi
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