[PATCH 3/3] drm/xe: Avoid shrinker reclaim from kswapd under fragmentation

[Matthew Brost <matthew.brost@intel.com>]

When the Xe shrinker is invoked from kswapd, a large amount of free
memory in ZONE_NORMAL relative to the high watermark is a strong signal
that reclaim is being driven by fragmentation rather than true memory
pressure.

In this case, shrinking Xe memory is unlikely to help kswapd make
forward progress. Instead it can evict active GPU memory despite the
system still having substantial free memory, increasing residency churn
and reducing GPU forward progress.

Detect this case and bail out early from the Xe shrinker when running in
kswapd and ZONE_NORMAL has more than 2x its high watermark free.

Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Carlos Santa <carlos.santa@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_shrinker.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_shrinker.c b/drivers/gpu/drm/xe/xe_shrinker.c
index 83374cd57660..e56afde83de6 100644
--- a/drivers/gpu/drm/xe/xe_shrinker.c
+++ b/drivers/gpu/drm/xe/xe_shrinker.c
@@ -236,6 +236,19 @@ static unsigned long xe_shrinker_scan(struct shrinker *shrink, struct shrink_con
 	if (nr_scanned >= nr_to_scan || !can_backup)
 		goto out;
 
+	if (current_is_kswapd()) {
+		struct zone *zone = &NODE_DATA(sc->nid)->node_zones[ZONE_NORMAL];
+		unsigned long free_pages = zone_page_state(zone, NR_FREE_PAGES);
+		unsigned long high_wmark = high_wmark_pages(zone);
+
+		/*
+		 * If we have 2x the high watermark free, this is definitely
+		 * fragmentation
+		 */
+		if (free_pages > (high_wmark * 2))
+			goto out;
+	}
+
 	/* If we didn't wake before, try to do it now if needed. */
 	if (!runtime_pm)
 		runtime_pm = xe_shrinker_runtime_pm_get(shrinker, true, 0, can_backup);
-- 
2.34.1