Add a beneficial_order_fault_inject debugfs fault attribute, mirroring backup_fault_inject, that forces allocation at (or above) the device's beneficial order to fail in __ttm_pool_alloc(). When triggered, both the pool take and the system page allocation are skipped for that order, so the allocation falls into the existing lower-the-order path that sets the TTM_TT_FLAG_BENEFICIAL_ORDER_FAILED tt page flag (and bails out with -ENOMEM for defrag moves).
This lets the TTM_TT_FLAG_BENEFICIAL_ORDER_FAILED tracking and the driver-side defrag path be exercised deterministically, without having to drive the system into real memory fragmentation to provoke a sub-optimal backing. The knob is registered at /sys/kernel/debug/ttm/beneficial_order_fault_inject and compiles out when CONFIG_FAULT_INJECTION is disabled. 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 | 35 ++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c index 340855e9bcfe..34f533adb8eb 100644 --- a/drivers/gpu/drm/ttm/ttm_pool.c +++ b/drivers/gpu/drm/ttm/ttm_pool.c @@ -53,6 +53,7 @@ #ifdef CONFIG_FAULT_INJECTION #include <linux/fault-inject.h> static DECLARE_FAULT_ATTR(backup_fault_inject); +static DECLARE_FAULT_ATTR(beneficial_order_fault_inject); #else #define should_fail(...) false #endif @@ -812,21 +813,34 @@ struct ttm_pool_alloc_iter { unsigned int order; enum ttm_caching page_caching; bool allow_pools; + bool fail_beneficial; struct page *p; }; /* * Acquire a single page for the current order, leaving it in @it->p (NULL on - * failure). Tries a same-order pool page, then a fresh system allocation. + * failure). Tries a same-order pool page, then a fresh system allocation. Fault + * injection can force the beneficial-order paths to "fail". */ static void ttm_pool_iter_acquire_page(struct ttm_pool_alloc_iter *it) { struct ttm_pool_type *pt; - /* First, try to allocate a page from a pool if one exists. */ it->p = NULL; + + /* + * Fault injection: pretend allocation at (or above) the device's + * beneficial order failed, forcing a sub-optimal backing. Exercises the + * beneficial_order_failed tracking and the driver defrag path without + * driving the system into real fragmentation. + */ + it->fail_beneficial = IS_ENABLED(CONFIG_FAULT_INJECTION) && + it->beneficial_order && it->order >= it->beneficial_order && + should_fail(&beneficial_order_fault_inject, 1); + + /* First, try to allocate a page from a pool if one exists. */ pt = ttm_pool_select_type(it->pool, it->page_caching, it->order); - if (!it->p && pt && it->allow_pools) + if (!it->p && pt && it->allow_pools && !it->fail_beneficial) it->p = ttm_pool_type_take(pt, ttm_pool_nid(it->pool)); /* @@ -834,7 +848,7 @@ static void ttm_pool_iter_acquire_page(struct ttm_pool_alloc_iter *it) * this also disallows additional pool allocations using write-back * cached pools of the same order. */ - if (!it->p) { + if (!it->p && !it->fail_beneficial) { it->page_caching = ttm_cached; it->allow_pools = false; it->p = ttm_pool_alloc_page(it->pool, it->gfp_flags, it->order, @@ -851,6 +865,9 @@ static void ttm_pool_iter_acquire_page(struct ttm_pool_alloc_iter *it) */ static int ttm_pool_iter_lower_order(struct ttm_pool_alloc_iter *it) { + bool at_beneficial = it->beneficial_order && + it->order == it->beneficial_order; + if (!it->order) return -ENOMEM; @@ -860,13 +877,16 @@ static int ttm_pool_iter_lower_order(struct ttm_pool_alloc_iter *it) * pages. Record it so the driver can later try to defragment the object * back to beneficial order. */ - if (it->beneficial_order && it->order == it->beneficial_order) { + if (it->fail_beneficial || at_beneficial) { it->tt->page_flags |= TTM_TT_FLAG_BENEFICIAL_ORDER_FAILED; if (it->ctx->defrag) return -ENOMEM; } - it->order--; + if (it->fail_beneficial) + it->order = it->beneficial_order - 1; + else + it->order--; it->page_caching = it->tt->caching; it->allow_pools = true; @@ -1536,6 +1556,9 @@ int ttm_pool_mgr_init(unsigned long num_pages) #ifdef CONFIG_FAULT_INJECTION fault_create_debugfs_attr("backup_fault_inject", ttm_debugfs_root, &backup_fault_inject); + fault_create_debugfs_attr("beneficial_order_fault_inject", + ttm_debugfs_root, + &beneficial_order_fault_inject); #endif #endif -- 2.34.1
