When __ttm_pool_alloc() fails to allocate a chunk at the device's beneficial order and falls back to a smaller order, the object ends up backed by a sub-optimal set of pages. Nothing currently records this, so a driver has no way to know an object would benefit from being re-backed with beneficial-order pages later.
Add a bool beneficial_order_failed to struct ttm_tt, initialised to false in ttm_tt_init_fields() and reset at the start of each fresh ttm_pool_alloc(). Set it in __ttm_pool_alloc() when an allocation at exactly the beneficial order fails before dropping to a lower order. Drivers can use this hint to queue the buffer object for later defragmentation. Cc: Carlos Santa <[email protected]> Cc: Ryan Neph <[email protected]> Cc: Christian Koenig <[email protected]> Cc: Huang Rui <[email protected]> Cc: Matthew Auld <[email protected]> Cc: Maarten Lankhorst <[email protected]> Cc: Maxime Ripard <[email protected]> Cc: Thomas Zimmermann <[email protected]> Cc: David Airlie <[email protected]> Cc: Simona Vetter <[email protected]> Cc: [email protected] Cc: [email protected] Cc: Thomas Hellström <[email protected]> Assisted-by: GitHub_Copilot:claude-opus-4.8 Signed-off-by: Matthew Brost <[email protected]> --- drivers/gpu/drm/ttm/ttm_pool.c | 11 +++++++++++ drivers/gpu/drm/ttm/ttm_tt.c | 1 + include/drm/ttm/ttm_tt.h | 8 ++++++++ 3 files changed, 20 insertions(+) diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c index 5b95f8f938f7..a1a74ccfcbf0 100644 --- a/drivers/gpu/drm/ttm/ttm_pool.c +++ b/drivers/gpu/drm/ttm/ttm_pool.c @@ -773,6 +773,7 @@ static int __ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt, struct ttm_pool_alloc_state *alloc, struct ttm_pool_tt_restore *restore) { + const unsigned int beneficial_order = ttm_pool_beneficial_order(pool); enum ttm_caching page_caching; gfp_t gfp_flags = GFP_USER; pgoff_t caching_divide; @@ -823,6 +824,15 @@ static int __ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt, /* If that fails, lower the order if possible and retry. */ if (!p) { if (order) { + /* + * Failing to allocate at the device's beneficial + * order means we are about to back this object + * with a sub-optimal (smaller order) set of + * pages. Record it so the driver can later try to + * defragment the object back to beneficial order. + */ + if (beneficial_order && order == beneficial_order) + tt->beneficial_order_failed = true; --order; page_caching = tt->caching; allow_pools = true; @@ -887,6 +897,7 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt, if (WARN_ON(ttm_tt_is_backed_up(tt))) return -EINVAL; + tt->beneficial_order_failed = false; ttm_pool_alloc_state_init(tt, &alloc); return __ttm_pool_alloc(pool, tt, ctx, &alloc, NULL); diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c index b645a1818184..27e09a58cf03 100644 --- a/drivers/gpu/drm/ttm/ttm_tt.c +++ b/drivers/gpu/drm/ttm/ttm_tt.c @@ -164,6 +164,7 @@ static void ttm_tt_init_fields(struct ttm_tt *ttm, ttm->caching = caching; ttm->restore = NULL; ttm->backup = NULL; + ttm->beneficial_order_failed = false; } int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo, diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h index 406437ad674b..55202362987a 100644 --- a/include/drm/ttm/ttm_tt.h +++ b/include/drm/ttm/ttm_tt.h @@ -126,6 +126,14 @@ struct ttm_tt { enum ttm_caching caching; /** @restore: Partial restoration from backup state. TTM private */ struct ttm_pool_tt_restore *restore; + /** + * @beneficial_order_failed: Set by the TTM pool allocator when at least + * one chunk that could have been allocated at the pool's beneficial + * order had to fall back to a smaller order. This indicates that a + * sub-optimal set of pages was chosen for this object, and can be used + * by drivers to queue the buffer object for later defragmentation. + */ + bool beneficial_order_failed; }; /** -- 2.34.1
