DGX OS 7.5.0 OTA (UEFI 5.36_0ACUM027): ~7.2 GiB less RAM available at boot

Accelerated Computing DGX Spark / GB10 User Forum DGX Spark / GB10
1

Summary
After the DGX OS 7.5.0 OTA (2026-09-13), the kernel reports ~7.2 GiB less RAM available at boot. The same OTA updated the UEFI firmware (5.36_0ACUM018 → 5.36_0ACUM027) and changed the DMI product string. The reduction is a boot-time firmware/memblock reservation, not a userspace process. No release note or forum post documents a change of this size.

System

  • DGX Spark Founders Edition, serial 1984825002667, host spark-2d58
  • Pre-OTA: DGX OS 7.2.3, kernel 6.11.0-1016-nvidia, UEFI 5.36_0ACUM018 (2025-09-09)
  • Post-OTA: DGX OS 7.5.0, kernel 7.0.0-1019-nvidia, UEFI 5.36_0ACUM027 (2026-06-12)

Evidence (kernel boot log Memory: line; consistent across all 9 retained boots)

  • Available: 125,269,464 K (119.5 GiB) → 117,723,484 K (112.3 GiB) = −7.20 GiB
  • Reserved: 8,403,760 K (8.01 GiB) → 16,079,932 K (15.33 GiB) = +7.32 GiB
  • Physical total unchanged: 133,828,484 K
  • Largest reserved RAM region: memblock 0x1d97c00000..0x1fe2dfffff (~9.2 GiB, RSV_KERN), unlabeled in /proc/iomem

Ruled out: userspace (system services ~1.1 GB RSS), kernel config diff, OTA-added cmdline params, IOMMU/SMMU/SWIOTLB.

Request

  1. Did UEFI 5.36_0ACUM027 intentionally increase a reserved carveout by ~7 GiB? Is there a firmware changelog?
  2. Is it adjustable via BIOS/firmware config, or required for GB10 GPU operation?
  3. Is there a supported way to reclaim it, or is it a tracked known issue?
2

Here’s a comparison on two FE Sparks with identical firmware:

|                  | Spark 1, kernel 7.0 | Spark 2, kernel 6.17 |
| ---------------- | ------------------: | -------------------: |
| Recognized RAM   |     133,828,484 KiB |      133,828,484 KiB |
| Boot “available” |     117,725,480 KiB |      127,347,964 KiB |
| `reserved`       |      16,079,772 KiB |        6,324,716 KiB |
| CMA              |                   0 |          131,072 KiB |
| CMA base         |                none |         `0xf2000000` |

There’s the ~9.3 GiB difference in reserved memory!

6.x kernel: ~6.0 GiB “reserved”
7.x kernel: ~15.3 GiB “reserved”

The kernel with CMA enable has more available RAM.

3

That sounds awful. Would be nice to know some ways to debloat.

4

Seems like there would be community firmware to make DGX Spark great (or less bad) again.

5
6

I guess the best question is, “how the hell do I stop my Spark from automatically updating” at this point. Clearly these updates weren’t tested at all and are cursed. I mostly boot headless, so I only have command line right now. How do I know if it tried to install any of this garbage?

7

You’ll probably be better off rolling back the kernel.

I’m not holding my breath, but it would still be nice to get an explanation from NVIDIA staff about the root cause.

Why does this even happen?

8

Probably Mr. Claude did it

9

The recent kernel upgrade also enabled Kexec HandOver (KHO) which increases reserved memory. Updates are rolling out to mitigate this issue and can take up to several hours to appear in some regions

10

I just updated normally and it’s working fine. No stability issues and no missing RAM.