| Memory in skiboot |
| ================= |
| |
| There are regions of memory we statically allocate for firmware as well as |
| a HEAP region for boot and runtime allocations. |
| |
| A design principle of skiboot is to attempt not to allocate memory at runtime, |
| or at least keep it to a minimum, and not do so in any critical code path |
| for the system to remain running. |
| |
| At no point during runtime should a skiboot memory allocation failure cause |
| the system to stop functioning. |
| |
| HEAP |
| ---- |
| |
| Dynamic memory allocations go in a single heap. This is identified as |
| Region ibm,firmware-heap and appears as a reserved section in the device tree. |
| |
| Originally, it was 12582912 bytes in size (declared in mem_map.h). |
| Now, it is 13631488 bytes after being bumped as part of the GCOV work. |
| |
| We increased heap size as on larger systems, we were getting close to using |
| all the heap once skiboot became 2MB with GCOV. |
| |
| Heap usage is printed before running the payload. |
| |
| For example, as of writing, on a dual socket Tuleta: :: |
| |
| [45215870591,5] SkiBoot skiboot-5.0.1-94-gb759ce2 starting... |
| [3680939340,5] CUPD: T side MI Keyword = SV830_027 |
| [3680942658,5] CUPD: T side ML Keyword = FW830.00 |
| [15404383291,5] Region ibm,firmware-heap free: 5378072 |
| |
| and on a palmetto: :: |
| |
| [24748502575,5] SkiBoot skiboot-5.0.1-94-gb759ce2 starting... |
| [9870429550,5] Region ibm,firmware-heap free: 10814856 |
| |
| Our memory allocator is simple, a use pattern of: :: |
| |
| A = malloc(); |
| B = malloc(); |
| free(A); |
| |
| is likely to generate fragmentation, so it should generally be avoided |
| where possible. |
