Re: [PATCH v2 1/9] mm/compaction: skip useless pfn when updating cached pfn

Vlastimil Babka
2015-08-24T09:07:23Z

On 08/24/2015 04:19 AM, Joonsoo Kim wrote:
> Cached pfn is used to determine the start position of scanner
> at next compaction run. Current cached pfn points the skipped pageblock
> so we uselessly checks whether pageblock is valid for compaction and
> skip-bit is set or not. If we set scanner's cached pfn to next pfn of
> skipped pageblock, we don't need to do this check.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
> mm/compaction.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 6ef2fdf..c2d3d6a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -261,10 +261,9 @@ void reset_isolation_suitable(pg_data_t *pgdat)
> */
> static void update_pageblock_skip(struct compact_control *cc,
> struct page *page, unsigned long nr_isolated,
> - bool migrate_scanner)
> + unsigned long pfn, bool migrate_scanner)
> {
> struct zone *zone = cc->zone;
> - unsigned long pfn;
>
> if (cc->ignore_skip_hint)
> return;
> @@ -277,8 +276,6 @@ static void update_pageblock_skip(struct compact_control *cc,
>
> set_pageblock_skip(page);
>
> - pfn = page_to_pfn(page);
> -
> /* Update where async and sync compaction should restart */
> if (migrate_scanner) {
> if (pfn > zone->compact_cached_migrate_pfn[0])
> @@ -300,7 +297,7 @@ static inline bool isolation_suitable(struct compact_control *cc,
>
> static void update_pageblock_skip(struct compact_control *cc,
> struct page *page, unsigned long nr_isolated,
> - bool migrate_scanner)
> + unsigned long pfn, bool migrate_scanner)
> {
> }
> #endif /* CONFIG_COMPACTION */
> @@ -509,7 +506,8 @@ isolate_fail:
>
> /* Update the pageblock-skip if the whole pageblock was scanned */
> if (blockpfn == end_pfn)
> - update_pageblock_skip(cc, valid_page, total_isolated, false);
> + update_pageblock_skip(cc, valid_page, total_isolated,
> + end_pfn, false);

In isolate_freepages_block() this means we actually go logically *back*
one pageblock, as the direction is opposite? I know it's not an issue
after the redesign patch so you wouldn't notice it when testing the
whole series. But there's a non-zero chance that the smaller fixes are
merged first and the redesign later...

>
> count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
> if (total_isolated)
> @@ -811,7 +809,8 @@ isolate_success:
> * if the whole pageblock was scanned without isolating any page.
> */
> if (low_pfn == end_pfn)
> - update_pageblock_skip(cc, valid_page, nr_isolated, true);
> + update_pageblock_skip(cc, valid_page, nr_isolated,
> + end_pfn, true);
>
> trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
> nr_scanned, nr_isolated);
>