[PATCH v2 5/5] 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 usable zones 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 any usable zone 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 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_shrinker.c b/drivers/gpu/drm/xe/xe_shrinker.c
index 83374cd57660..e28e5e90c198 100644
--- a/drivers/gpu/drm/xe/xe_shrinker.c
+++ b/drivers/gpu/drm/xe/xe_shrinker.c
@@ -236,6 +236,9 @@ static unsigned long xe_shrinker_scan(struct shrinker *shrink, struct shrink_con
 	if (nr_scanned >= nr_to_scan || !can_backup)
 		goto out;
 
+	if (ttm_bo_shrink_kswap_fragmented(sc->nid))
+		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