[PATCH] drm: i915: use kzalloc_flex

[PATCH] drm: i915: use kzalloc_flex

[Rosen Penev]

Simplifies allocations by using a flexible array member in this struct.
No need to free separately.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/gpu/drm/i915/gt/intel_gtt.h   |  2 +-
 drivers/gpu/drm/i915/gt/intel_ppgtt.c | 15 +--------------
 2 files changed, 2 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
index f6f223090760..49b2d2d24fd8 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.h
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
@@ -187,7 +187,7 @@ struct i915_page_table {
 struct i915_page_directory {
 	struct i915_page_table pt;
 	spinlock_t lock;
-	void **entry;
+	void *entry[];
 };
 
 #define __px_choose_expr(x, type, expr, other) \
diff --git a/drivers/gpu/drm/i915/gt/intel_ppgtt.c b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
index 72d8473a448b..20cc59a005c9 100644
--- a/drivers/gpu/drm/i915/gt/intel_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
@@ -36,16 +36,10 @@ struct i915_page_directory *__alloc_pd(int count)
 {
 	struct i915_page_directory *pd;
 
-	pd = kzalloc_obj(*pd, I915_GFP_ALLOW_FAIL);
+	pd = kzalloc_flex(*pd, entry, count, I915_GFP_ALLOW_FAIL);
 	if (unlikely(!pd))
 		return NULL;
 
-	pd->entry = kzalloc_objs(*pd->entry, count, I915_GFP_ALLOW_FAIL);
-	if (unlikely(!pd->entry)) {
-		kfree(pd);
-		return NULL;
-	}
-
 	spin_lock_init(&pd->lock);
 	return pd;
 }
@@ -60,7 +54,6 @@ struct i915_page_directory *alloc_pd(struct i915_address_space *vm)
 
 	pd->pt.base = vm->alloc_pt_dma(vm, I915_GTT_PAGE_SIZE_4K);
 	if (IS_ERR(pd->pt.base)) {
-		kfree(pd->entry);
 		kfree(pd);
 		return ERR_PTR(-ENOMEM);
 	}
@@ -72,12 +65,6 @@ void free_px(struct i915_address_space *vm, struct i915_page_table *pt, int lvl)
 {
 	BUILD_BUG_ON(offsetof(struct i915_page_directory, pt));
 
-	if (lvl) {
-		struct i915_page_directory *pd =
-			container_of(pt, typeof(*pd), pt);
-		kfree(pd->entry);
-	}
-
 	if (pt->base)
 		i915_gem_object_put(pt->base);
 
-- 
2.54.0

Re: [PATCH] drm: i915: use kzalloc_flex

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Flexible array conversion forces inefficient order-1 (8KB) allocations for page directories.
--

commit ed37e64eb293a3ef09353d34ef014044171cfe28
Author: Rosen Penev <rosenp@gmail.com>
drm: i915: use kzalloc_flex

This patch simplifies the allocation of i915_page_directory structures by
replacing a pointer with a flexible array member, consolidating two
allocations into one.

> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
> index b54ee4f25af10..642b5c856a55a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
> @@ -186,7 +186,7 @@ struct i915_page_table {
>  struct i915_page_directory {
>  	struct i915_page_table pt;
>  	spinlock_t lock;
> -	void **entry;
> +	void *entry[];
>  };
>  
>  #define __px_choose_expr(x, type, expr, other) \
> diff --git a/drivers/gpu/drm/i915/gt/intel_ppgtt.c b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> index 72d8473a448b9..20cc59a005c97 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> @@ -36,16 +36,10 @@ struct i915_page_directory *__alloc_pd(int count)
>  {
>  	struct i915_page_directory *pd;
>  
> -	pd = kzalloc_obj(*pd, I915_GFP_ALLOW_FAIL);
> +	pd = kzalloc_flex(*pd, entry, count, I915_GFP_ALLOW_FAIL);

[Severity: High]
Does this flexible array conversion force inefficient order-1 (8KB)
allocations for page directories?

Consolidating the entry array into struct i915_page_directory pushes the
allocation size from exactly 4096 bytes (for the array) to 4128 bytes. The
base struct is roughly 32 bytes, plus 512 * 8 bytes for the flexible array.

On systems with 4KB pages (like x86), a 4128-byte request cannot be satisfied
by the kmalloc-4k cache and spills over to the kmalloc-8k cache. This requires
an order-1 page allocation, wasting 4064 bytes per page directory and
significantly increasing the risk of allocation failures under memory
fragmentation compared to the previous order-0 allocation.

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260630011907.1453253-1-rosenp@gmail.com?part=1

✗ LGCI.VerificationFailed: failure for drm: i915: use kzalloc_flex

[Patchwork]

== Series Details ==

Series: drm: i915: use kzalloc_flex
URL   : https://patchwork.freedesktop.org/series/169617/
State : failure

== Summary ==

Series author address 'rosenp@gmail.com' is not on the allowlist, which prevents CI from being automatically triggered.
If you want CI to run for this series, ask Patchwork project owners to click 'retest' on the series in Patchwork.
Exception occurred during validation, bailing out!
Build URL: http://gfx-ci.igk.intel.com:8080/job/CI_PW_kernel/180290/ (on built-in)