Re: [PATCH v2] drm/xe: Convert stolen memory over to ttm_range_manager

Maarten Lankhorst
2026-04-16T15:33:37Z

Hey,

Den 2026-04-16 kl. 17:19, skrev Sanjay Yadav:
> Stolen memory requires physically contiguous allocations for display
> scanout and compressed framebuffers. The stolen memory manager was
> sharing the gpu_buddy allocator backend with the VRAM manager, but
> buddy manages non-contiguous power-of-two blocks making it a poor fit.
> Stolen memory also has fundamentally different allocation patterns:
>
> - Allocation sizes are not power-of-two. Since buddy rounds up to the
> next power-of-two block size, a ~17MB request can fail even with
> ~22MB free, because the free space is fragmented across non-fitting
> power-of-two blocks.
> - Hardware restrictions prevent using the first 4K page of stolen for
> certain allocations (e.g., FBC). The display code sets fpfn=1 to
> enforce this, but when fpfn != 0, gpu_buddy enables
> GPU_BUDDY_RANGE_ALLOCATION mode which disables the try_harder
> coalescing path, further reducing allocation success.
>
> This combination caused FBC compressed framebuffer (CFB) allocation
> failures on platforms like NVL/PTL. In case of NVL where stolen memory
> is ~56MB and the initial plane framebuffer consumes ~34MB at probe time,
> leaving ~22MB for subsequent allocations.
>
> Use ttm_range_man_init_nocheck() to set up a drm_mm-backed TTM resource
> manager for stolen memory. This reuses the TTM core's ttm_range_manager
> callbacks, avoiding duplicate implementations.
>
> Tested on NVL with a 4K DP display: stolen_mm shows a single ~22MB
> contiguous free hole after initial plane framebuffer allocation, and
> FBC successfully allocates its CFB from that region. The corresponding
> IGT was previously skipped and now passes.
>
> v2:
> - Clarify that stolen memory requires contiguous allocations (Matt B)
> - Properly handle xe_ttm_resource_visible() for stolen instead of
> unconditionally returning true (Matt A)
>
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7631
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Suggested-by: Matthew Auld <matthew.auld@intel.com>
> Assisted-by: GitHub Copilot:claude-sonnet-4.6
> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
> ---
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

The changes look good, I never considered the differences between the
buddy allocator and range manager. Glad to see this works a lot better!

One thing I did notice that in most cases, is there any reason for the
range manager to use pages? It should be able to use bytes and remove
a lot of shifts to convert between bytes and pages in the code.

> drivers/gpu/drm/xe/xe_bo.c | 16 +++++--
> drivers/gpu/drm/xe/xe_device_types.h | 3 ++
> drivers/gpu/drm/xe/xe_res_cursor.h | 14 +++++-
> drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c | 64 +++++++++-----------------
> drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h | 9 ++++
> drivers/gpu/drm/xe/xe_ttm_vram_mgr.c | 11 ++---
> 6 files changed, 63 insertions(+), 54 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index a7c2dc7f224c..b737edf04d60 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -599,11 +599,17 @@ static void xe_ttm_tt_destroy(struct ttm_device *ttm_dev, struct ttm_tt *tt)
> kfree(tt);
> }
>
> -static bool xe_ttm_resource_visible(struct ttm_resource *mem)
> +static bool xe_ttm_resource_visible(struct xe_device *xe, struct ttm_resource *mem)
> {
> - struct xe_ttm_vram_mgr_resource *vres =
> - to_xe_ttm_vram_mgr_resource(mem);
> + struct xe_ttm_vram_mgr_resource *vres;
>
> + if (mem->mem_type == XE_PL_STOLEN) {
> + struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
> +
> + return mgr->io_base && !xe_ttm_stolen_cpu_access_needs_ggtt(xe);
> + }
> +
> + vres = to_xe_ttm_vram_mgr_resource(mem);
> return vres->used_visible_size == mem->size;
> }
>
> @@ -621,7 +627,7 @@ bool xe_bo_is_visible_vram(struct xe_bo *bo)
> if (drm_WARN_ON(bo->ttm.base.dev, !xe_bo_is_vram(bo)))
> return false;
>
> - return xe_ttm_resource_visible(bo->ttm.resource);
> + return xe_ttm_resource_visible(xe_bo_device(bo), bo->ttm.resource);
> }
>
> static int xe_ttm_io_mem_reserve(struct ttm_device *bdev,
> @@ -637,7 +643,7 @@ static int xe_ttm_io_mem_reserve(struct ttm_device *bdev,
> case XE_PL_VRAM1: {
> struct xe_vram_region *vram = res_to_mem_region(mem);
>
> - if (!xe_ttm_resource_visible(mem))
> + if (!xe_ttm_resource_visible(xe, mem))
> return -EINVAL;
>
> mem->bus.offset = mem->start << PAGE_SHIFT;
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
> index 150c76b2acaf..ffb84659c413 100644
> --- a/drivers/gpu/drm/xe/xe_device_types.h
> +++ b/drivers/gpu/drm/xe/xe_device_types.h
> @@ -42,6 +42,7 @@ struct xe_ggtt;
> struct xe_i2c;
> struct xe_pat_ops;
> struct xe_pxp;
> +struct xe_ttm_stolen_mgr;
> struct xe_vram_region;
>
> /**
> @@ -278,6 +279,8 @@ struct xe_device {
> struct ttm_resource_manager sys_mgr;
> /** @mem.sys_mgr: system memory shrinker. */
> struct xe_shrinker *shrinker;
> + /** @mem.stolen_mgr: stolen memory manager. */
> + struct xe_ttm_stolen_mgr *stolen_mgr;
> } mem;
>
> /** @sriov: device level virtualization data */
> diff --git a/drivers/gpu/drm/xe/xe_res_cursor.h b/drivers/gpu/drm/xe/xe_res_cursor.h
> index 5f4ab08c0686..0522caafd89d 100644
> --- a/drivers/gpu/drm/xe/xe_res_cursor.h
> +++ b/drivers/gpu/drm/xe/xe_res_cursor.h
> @@ -101,7 +101,15 @@ static inline void xe_res_first(struct ttm_resource *res,
> cur->mem_type = res->mem_type;
>
> switch (cur->mem_type) {
> - case XE_PL_STOLEN:
> + case XE_PL_STOLEN: {
> + /* res->start is in pages (ttm_range_manager). */
> + cur->start = (res->start << PAGE_SHIFT) + start;
> + cur->size = size;
> + cur->remaining = size;
> + cur->node = NULL;
> + cur->mm = NULL;
> + break;
> + }
> case XE_PL_VRAM0:
> case XE_PL_VRAM1: {
> struct gpu_buddy_block *block;
> @@ -289,6 +297,10 @@ static inline void xe_res_next(struct xe_res_cursor *cur, u64 size)
>
> switch (cur->mem_type) {
> case XE_PL_STOLEN:
> + /* Just advance within the contiguous region. */
> + cur->start += size;
> + cur->size = cur->remaining;
> + break;
> case XE_PL_VRAM0:
> case XE_PL_VRAM1:
> start = size - cur->size;
> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> index 27c9d72222cf..5e9070739e65 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> @@ -19,30 +19,11 @@
> #include "xe_device.h"
> #include "xe_gt_printk.h"
> #include "xe_mmio.h"
> -#include "xe_res_cursor.h"
> #include "xe_sriov.h"
> #include "xe_ttm_stolen_mgr.h"
> -#include "xe_ttm_vram_mgr.h"
> #include "xe_vram.h"
> #include "xe_wa.h"
>
> -struct xe_ttm_stolen_mgr {
> - struct xe_ttm_vram_mgr base;
> -
> - /* PCI base offset */
> - resource_size_t io_base;
> - /* GPU base offset */
> - resource_size_t stolen_base;
> -
> - void __iomem *mapping;
> -};
> -
> -static inline struct xe_ttm_stolen_mgr *
> -to_stolen_mgr(struct ttm_resource_manager *man)
> -{
> - return container_of(man, struct xe_ttm_stolen_mgr, base.manager);
> -}
> -
> /**
> * xe_ttm_stolen_cpu_access_needs_ggtt() - If we can't directly CPU access
> * stolen, can we then fallback to mapping through the GGTT.
> @@ -210,12 +191,19 @@ static u64 detect_stolen(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
> #endif
> }
>
> +static void xe_ttm_stolen_mgr_fini(struct drm_device *dev, void *arg)
> +{
> + struct xe_device *xe = to_xe_device(dev);
> +
> + ttm_range_man_fini_nocheck(&xe->ttm, XE_PL_STOLEN);
> +}
> +
> int xe_ttm_stolen_mgr_init(struct xe_device *xe)
> {
> struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> struct xe_ttm_stolen_mgr *mgr;
> u64 stolen_size, io_size;
> - int err;
> + int ret;
>
> mgr = drmm_kzalloc(&xe->drm, sizeof(*mgr), GFP_KERNEL);
> if (!mgr)
> @@ -244,12 +232,12 @@ int xe_ttm_stolen_mgr_init(struct xe_device *xe)
> if (mgr->io_base && !xe_ttm_stolen_cpu_access_needs_ggtt(xe))
> io_size = stolen_size;
>
> - err = __xe_ttm_vram_mgr_init(xe, &mgr->base, XE_PL_STOLEN, stolen_size,
> - io_size, PAGE_SIZE);
> - if (err) {
> - drm_dbg_kms(&xe->drm, "Stolen mgr init failed: %i\n", err);
> - return err;
> - }
> + ret = ttm_range_man_init_nocheck(&xe->ttm, XE_PL_STOLEN, false,
> + stolen_size >> PAGE_SHIFT);
> + if (ret)
> + return ret;
> +
> + xe->mem.stolen_mgr = mgr;
>
> drm_dbg_kms(&xe->drm, "Initialized stolen memory support with %llu bytes\n",
> stolen_size);
> @@ -257,36 +245,32 @@ int xe_ttm_stolen_mgr_init(struct xe_device *xe)
> if (io_size)
> mgr->mapping = devm_ioremap_wc(&pdev->dev, mgr->io_base, io_size);
>
> - return 0;
> + return drmm_add_action_or_reset(&xe->drm, xe_ttm_stolen_mgr_fini, mgr);
> }
>
> u64 xe_ttm_stolen_io_offset(struct xe_bo *bo, u32 offset)
> {
> struct xe_device *xe = xe_bo_device(bo);
> - struct ttm_resource_manager *ttm_mgr = ttm_manager_type(&xe->ttm, XE_PL_STOLEN);
> - struct xe_ttm_stolen_mgr *mgr = to_stolen_mgr(ttm_mgr);
> - struct xe_res_cursor cur;
> + struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
>
> XE_WARN_ON(!mgr->io_base);
>
> if (xe_ttm_stolen_cpu_access_needs_ggtt(xe))
> return mgr->io_base + xe_bo_ggtt_addr(bo) + offset;
>
> - xe_res_first(bo->ttm.resource, offset, 4096, &cur);
> - return mgr->io_base + cur.start;
> + /* Range allocator: res->start is in pages. */
> + return mgr->io_base + (bo->ttm.resource->start << PAGE_SHIFT) + offset;
> }
>
> static int __xe_ttm_stolen_io_mem_reserve_bar2(struct xe_device *xe,
> struct xe_ttm_stolen_mgr *mgr,
> struct ttm_resource *mem)
> {
> - struct xe_res_cursor cur;
> -
> if (!mgr->io_base)
> return -EIO;
>
> - xe_res_first(mem, 0, 4096, &cur);
> - mem->bus.offset = cur.start;
> + /* Range allocator always produces contiguous allocations. */
> + mem->bus.offset = mem->start << PAGE_SHIFT;
>
> drm_WARN_ON(&xe->drm, !(mem->placement & TTM_PL_FLAG_CONTIGUOUS));
>
> @@ -329,8 +313,7 @@ static int __xe_ttm_stolen_io_mem_reserve_stolen(struct xe_device *xe,
>
> int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem)
> {
> - struct ttm_resource_manager *ttm_mgr = ttm_manager_type(&xe->ttm, XE_PL_STOLEN);
> - struct xe_ttm_stolen_mgr *mgr = ttm_mgr ? to_stolen_mgr(ttm_mgr) : NULL;
> + struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
>
> if (!mgr || !mgr->io_base)
> return -EIO;
> @@ -343,8 +326,5 @@ int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem)
>
> u64 xe_ttm_stolen_gpu_offset(struct xe_device *xe)
> {
> - struct xe_ttm_stolen_mgr *mgr =
> - to_stolen_mgr(ttm_manager_type(&xe->ttm, XE_PL_STOLEN));
> -
> - return mgr->stolen_base;
> + return xe->mem.stolen_mgr->stolen_base;
> }
> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> index 8e877d1e839b..049e91e77326 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
> @@ -12,6 +12,15 @@ struct ttm_resource;
> struct xe_bo;
> struct xe_device;
>
> +struct xe_ttm_stolen_mgr {
> + /* PCI base offset */
> + resource_size_t io_base;
> + /* GPU base offset */
> + resource_size_t stolen_base;
> +
> + void __iomem *mapping;
> +};
> +
> int xe_ttm_stolen_mgr_init(struct xe_device *xe);
> int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem);
> bool xe_ttm_stolen_cpu_access_needs_ggtt(struct xe_device *xe);
> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> index 5fd0d5506a7e..79ef8e1b5e5c 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> @@ -301,14 +301,13 @@ int __xe_ttm_vram_mgr_init(struct xe_device *xe, struct xe_ttm_vram_mgr *mgr,
> u64 default_page_size)
> {
> struct ttm_resource_manager *man = &mgr->manager;
> + const char *name;
> int err;
>
> - if (mem_type != XE_PL_STOLEN) {
> - const char *name = mem_type == XE_PL_VRAM0 ? "vram0" : "vram1";
> - man->cg = drmm_cgroup_register_region(&xe->drm, name, size);
> - if (IS_ERR(man->cg))
> - return PTR_ERR(man->cg);
> - }
> + name = mem_type == XE_PL_VRAM0 ? "vram0" : "vram1";
> + man->cg = drmm_cgroup_register_region(&xe->drm, name, size);
> + if (IS_ERR(man->cg))
> + return PTR_ERR(man->cg);
>
> man->func = &xe_ttm_vram_mgr_func;
> mgr->mem_type = mem_type;