[RFC PATCH 16/26] mm: compaction: improve compaction_suitable() accuracy

Johannes Weiner
2023-04-18T19:15:08Z

With the new per-mt free counts, compaction can check the watermarks
specifically against suitable migration targets. This ensures reclaim
keeps going when the free pages are in blocks that aren't actually
suitable migration targets: MIGRATE_FREE, UNMOVABLE, RECLAIMABLE.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/compaction.c | 23 +++++++++++++++--------
mm/vmscan.c | 7 +++++--
2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index b9eed0d43403..f637b4ed7f3c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2226,11 +2226,17 @@ enum compact_result compaction_suitable(struct zone *zone, int order,
unsigned int alloc_flags,
int highest_zoneidx)
{
+ unsigned long free_pages;
enum compact_result ret;
int fragindex;

- ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
- zone_page_state(zone, NR_FREE_PAGES));
+ /* Suitable migration targets */
+ free_pages = zone_page_state(zone, NR_FREE_MOVABLE);
+ free_pages += zone_page_state(zone, NR_FREE_CMA_PAGES);
+
+ ret = __compaction_suitable(zone, order, alloc_flags,
+ highest_zoneidx, free_pages);
+
/*
* fragmentation index determines if allocation failures are due to
* low memory or external fragmentation
@@ -2273,19 +2279,20 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
ac->highest_zoneidx, ac->nodemask) {
unsigned long available;
- enum compact_result compact_result;

+ available = zone_page_state_snapshot(zone, NR_FREE_MOVABLE);
+ available += zone_page_state_snapshot(zone, NR_FREE_CMA_PAGES);
/*
* Do not consider all the reclaimable memory because we do not
* want to trash just for a single high order allocation which
* is even not guaranteed to appear even if __compaction_suitable
* is happy about the watermark check.
*/
- available = zone_reclaimable_pages(zone) / order;
- available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
- compact_result = __compaction_suitable(zone, order, alloc_flags,
- ac->highest_zoneidx, available);
- if (compact_result == COMPACT_CONTINUE)
+ available += zone_reclaimable_pages(zone) / order;
+
+ if (__compaction_suitable(zone, order, alloc_flags,
+ ac->highest_zoneidx,
+ available) == COMPACT_CONTINUE)
return true;
}

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5b7b8d4f5297..9ecf29f4dab8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -6270,6 +6270,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
{
unsigned long watermark;
+ unsigned long free_pages;
enum compact_result suitable;

suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
@@ -6290,8 +6291,10 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
* we are already above the high+gap watermark, don't reclaim at all.
*/
watermark = high_wmark_pages(zone) + compact_gap(sc->order);
-
- return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
+ free_pages = zone_page_state_snapshot(zone, NR_FREE_MOVABLE);
+ free_pages += zone_page_state_snapshot(zone, NR_FREE_CMA_PAGES);
+ return __zone_watermark_ok(zone, 0, watermark, sc->reclaim_idx,
+ ALLOC_CMA, free_pages);
}

static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
--
2.39.2