STRUCT __DRM_I915_MEMORY_REGION_INFO(9)

💖 struct __drm_i915_memory_region_info(9) — Kernel API Manual 💖

okay so this is a page from the Kernel API Manual, and it's literally all about one little struct that tells you everything the driver knows about a memory region. bestie, it's giving "backstage pass to your GPU's brain" energy 🧠✨

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🌸 NAME 🌸

struct __drm_i915_memory_region_info — describes one region as known to the driver 🫶

✨ SYNOPSIS ✨

struct __drm_i915_memory_region_info {
    struct drm_i915_gem_memory_class_instance region;
    __u32 rsvd0;
    __u64 probed_size;
    __u64 unallocated_size;
    union {
      __u64 rsvd1[8];
      struct {
        __u64 probed_cpu_visible_size;
        __u64 unallocated_cpu_visible_size;
      };
    };
 };

no cap, that's the whole vibe of it 👑

🎀 Members 🎀

• region — the class:instance pair encoding 💅 that's the ID card for the region, basically.
• rsvd0 — MBZ. (that's "must be zero" — don't be the main character who fills it in 🙈)
• probed_size — memory probed by the driver ⭐

lowkey important: it should not be possible to ever encounter a zero value here, and also note that no current region type will ever return -1 here. for future region types though, that might be a possibility. and the same applies to the other size fields, iykyk.

• unallocated_size — estimate of memory remaining 🍓

fr fr, this one requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable accounting. without that (or if this is an older kernel) the value here will always equal the probed_size. also note this is only currently tracked for I915_MEMORY_CLASS_DEVICE regions — for other types the value here will always equal the probed_size.

• {unnamed_union} — anonymous 🫥 (yes literally anonymous, it's a mystery girlie)
• rsvd1 — MBZ 💀 again: must be zero. hands off.
• {unnamed_struct} — anonymous 🌈 (another anonymous one, we love a private queen)
• probed_cpu_visible_size — memory probed by the driver that is CPU accessible 💜

this will always be <= probed_size, and the remainder (if there is any) will not be CPU accessible.

on systems without small BAR, the probed_size will always equal the probed_cpu_visible_size, since all of it will be CPU accessible ✨

note this is only tracked for I915_MEMORY_CLASS_DEVICE regions (for other types the value here will always equal the probed_size).

and bestie listen: if the value returned here is zero, then this must be an old kernel which lacks the relevant small-bar uAPI support (including I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS), but on such systems we should never actually end up with a small BAR configuration, assuming we are able to load the kernel module. hence it should be safe to treat this the same as when probed_cpu_visible_size == probed_size. 🧚

• unallocated_cpu_visible_size — estimate of CPU visible memory remaining 💖

note this is only tracked for I915_MEMORY_CLASS_DEVICE regions (for other types the value here will always equal the probed_cpu_visible_size).

requires CAP_PERFMON or CAP_SYS_ADMIN to get reliable accounting. without this the value here will always equal the probed_cpu_visible_size. and note this is only currently tracked for I915_MEMORY_CLASS_DEVICE regions (for other types the value here will also always equal the probed_cpu_visible_size).

if this is an older kernel the value here will be zero, see also probed_cpu_visible_size. 😭

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🦋 Description 🦋

okay so heads up: this is using both struct drm_i915_query_item and struct drm_i915_query 🫶. for this new query we're adding the new query id DRM_I915_QUERY_MEMORY_REGIONS at drm_i915_query_item.query_id. slay, that's the whole plot 🔥

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👑 SEE ALSO 👑

kernel file ./Documentation/gpu/rfc/i915_small_bar.h struct __drm_i915_gem_create_ext(9) 📚

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and that's the tea, bestie 🍵💅 this page came from ./Documentation/gpu/rfc, dated October 2026, and it's filed under struct __drm..._region_info(9) — go off, you icon 🌟🎀