[PATCH v2 16/33] drm/xe: Back off beneficial-order reclaim under defrag pressure

[Matthew Brost]

Once a meaningful number of BOs are already tracked as being backed at a
sub-optimal order, continuing to push hard for beneficial-order pages
during populate mostly wastes time in reclaim/compaction.

In xe_ttm_tt_populate(), set ctx->beneficial_reclaim_backoff when the
device defrag count reaches XE_BO_DEFRAG_RECLAIM_BACKOFF_THRESHOLD (2)
so the TTM pool backs off and allocations make forward progress. The
deferred defrag pass is responsible for upgrading these objects to
beneficial order later.

Cc: Carlos Santa <carlos.santa@xxxxxxxxx>
Cc: Ryan Neph <ryanneph@xxxxxxxxxx>
Cc: Christian Koenig <christian.koenig@xxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Simona Vetter <simona@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Assisted-by: GitHub_Copilot:claude-opus-4.8
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
 drivers/gpu/drm/xe/xe_bo.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index d7b0536564ab..21d087170ef3 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -41,6 +41,14 @@
 #include "xe_vm.h"
 #include "xe_vram_types.h"
 
+/*
+ * Once this many BOs are tracked on the device defrag list (i.e. were backed
+ * with a sub-optimal page order), request that the TTM pool backs off from
+ * aggressive reclaim at the beneficial order during populate, so that
+ * allocations make forward progress instead of stalling.
+ */
+#define XE_BO_DEFRAG_RECLAIM_BACKOFF_THRESHOLD	2
+
 const char *const xe_mem_type_to_name[TTM_NUM_MEM_TYPES]  = {
 	[XE_PL_SYSTEM] = "system",
 	[XE_PL_TT] = "gtt",
@@ -598,6 +606,12 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt,
 	if (ttm_tt_is_backed_up(tt) && !xe_tt->purgeable) {
 		err = ttm_tt_restore(ttm_dev, tt, ctx);
 	} else {
+		struct xe_device *xe = ttm_to_xe_device(ttm_dev);
+
+		if (atomic_read(&xe->mem.defrag.count) >=
+		    XE_BO_DEFRAG_RECLAIM_BACKOFF_THRESHOLD)
+			ctx->beneficial_reclaim_backoff = true;
+
 		ttm_tt_clear_backed_up(tt);
 		err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx);
 	}
-- 
2.34.1