feat(mm): migrate to PageAlloc, FrameAlloc #2002

mkroening · 2025-10-21T14:14:50Z

Similar to #1994, this makes the internals of the physical and virtual memory allocation private. Note that this will slow down parts of paging right now, since it is not possible to hold a global FrameAlloc lock anymore. This means the lock has to be reacquired again and again until we improve the paging code or the FrameAlloc code.

Depends on #2008.
Closes #1994.

github-actions

Benchmark Results

Benchmark	Current: `82ea5fa`	Previous: `cb0d623`	Performance Ratio
startup_benchmark Build Time	`117.40` s	`111.98` s	`1.05`
startup_benchmark File Size	`0.91` MB	`0.89` MB	`1.01`
Startup Time - 1 core	`0.92` s (`±0.04` s)	`0.91` s (`±0.05` s)	`1.02`
Startup Time - 2 cores	`0.92` s (`±0.02` s)	`0.92` s (`±0.04` s)	`1.00`
Startup Time - 4 cores	`0.93` s (`±0.04` s)	`0.92` s (`±0.03` s)	`1.01`
multithreaded_benchmark Build Time	`111.51` s	`114.79` s	`0.97`
multithreaded_benchmark File Size	`1.01` MB	`1.00` MB	`1.01`
Multithreaded Pi Efficiency - 2 Threads	`87.01` % (`±8.29` %)	`90.02` % (`±8.17` %)	`0.97`
Multithreaded Pi Efficiency - 4 Threads	`42.65` % (`±3.92` %)	`44.54` % (`±3.42` %)	`0.96`
Multithreaded Pi Efficiency - 8 Threads	`24.76` % (`±2.15` %)	`25.97` % (`±2.04` %)	`0.95`
micro_benchmarks Build Time	`268.31` s	`261.23` s	`1.03`
micro_benchmarks File Size	`1.01` MB	`1.01` MB	`1.01`
Scheduling time - 1 thread	`137.72` ticks (`±38.01` ticks)	`140.01` ticks (`±34.10` ticks)	`0.98`
Scheduling time - 2 threads	`66.64` ticks (`±21.23` ticks)	`85.24` ticks (`±13.44` ticks)	`0.78`
Micro - Time for syscall (getpid)	`7.98` ticks (`±3.83` ticks)	`8.13` ticks (`±3.54` ticks)	`0.98`
Memcpy speed - (built_in) block size 4096	`58267.02` MByte/s (`±41456.38` MByte/s)	`58334.21` MByte/s (`±41243.72` MByte/s)	`1.00`
Memcpy speed - (built_in) block size 1048576	`18562.17` MByte/s (`±15848.52` MByte/s)	`21033.07` MByte/s (`±18225.52` MByte/s)	`0.88`
Memcpy speed - (built_in) block size 16777216	`9980.77` MByte/s (`±8442.52` MByte/s)	`13267.84` MByte/s (`±10774.63` MByte/s)	`0.75`
Memset speed - (built_in) block size 4096	`58343.14` MByte/s (`±41504.33` MByte/s)	`58219.36` MByte/s (`±41164.23` MByte/s)	`1.00`
Memset speed - (built_in) block size 1048576	`18945.24` MByte/s (`±16015.81` MByte/s)	`21368.76` MByte/s (`±18349.64` MByte/s)	`0.89`
Memset speed - (built_in) block size 16777216	`10202.92` MByte/s (`±8573.73` MByte/s)	`13479.15` MByte/s (`±10870.12` MByte/s)	`0.76`
Memcpy speed - (rust) block size 4096	`52549.24` MByte/s (`±39182.08` MByte/s)	`52819.55` MByte/s (`±38638.93` MByte/s)	`0.99`
Memcpy speed - (rust) block size 1048576	`19277.35` MByte/s (`±16375.41` MByte/s)	`23393.82` MByte/s (`±21095.61` MByte/s)	`0.82`
Memcpy speed - (rust) block size 16777216	`9441.37` MByte/s (`±7789.00` MByte/s)	`13873.33` MByte/s (`±11633.55` MByte/s)	`0.68`
Memset speed - (rust) block size 4096	`52880.95` MByte/s (`±39398.72` MByte/s)	`54298.23` MByte/s (`±39297.25` MByte/s)	`0.97`
Memset speed - (rust) block size 1048576	`19478.64` MByte/s (`±16458.84` MByte/s)	`23892.19` MByte/s (`±21294.83` MByte/s)	`0.82`
Memset speed - (rust) block size 16777216	`9745.15` MByte/s (`±8043.22` MByte/s)	`13997.13` MByte/s (`±11673.08` MByte/s)	`0.70`
alloc_benchmarks Build Time	`253.43` s	`250.66` s	`1.01`
alloc_benchmarks File Size	`0.97` MB	`0.96` MB	`1.01`
Allocations - Allocation success	`100.00` %	`100.00` %	`1`
Allocations - Deallocation success	`100.00` %	`100.00` %	`1`
Allocations - Pre-fail Allocations	`100.00` %	`100.00` %	`1`
Allocations - Average Allocation time	`10995.00` Ticks (`±2766.35` Ticks)	`8836.57` Ticks (`±1388.50` Ticks)	`1.24`
Allocations - Average Allocation time (no fail)	`10995.00` Ticks (`±2766.35` Ticks)	`8836.57` Ticks (`±1388.50` Ticks)	`1.24`
Allocations - Average Deallocation time	`2069.86` Ticks (`±340.76` Ticks)	`1396.33` Ticks (`±193.31` Ticks)	`1.48`
mutex_benchmark Build Time	`243.91` s	`245.80` s	`0.99`
mutex_benchmark File Size	`1.02` MB	`1.01` MB	`1.01`
Mutex Stress Test Average Time per Iteration - 1 Threads	`27.98` ns (`±6.03` ns)	`27.14` ns (`±5.97` ns)	`1.03`
Mutex Stress Test Average Time per Iteration - 2 Threads	`25.12` ns (`±2.97` ns)	`25.02` ns (`±3.35` ns)	`1.00`

This comment was automatically generated by workflow using github-action-benchmark.

mkroening · 2025-10-22T14:28:30Z

@m-mueller678, what do you think about PageAlloc and FrameAlloc instead of going back to free-standing functions? Feel free to review. :)

m-mueller678

Looks good to me, safe for the few split unsafe blocks. I like the change from free functions to methods.

m-mueller678 · 2025-10-22T14:46:55Z

src/arch/riscv64/mm/mod.rs

 pub fn init() {
-	crate::mm::physicalmem::init();
-	crate::mm::virtualmem::init();
+	unsafe {


could be merged into a single unsafe block

Having these operations in separate blocks was on purpose. See clippy::multiple_unsafe_ops_per_block. Arguably, the situation is far from ideal in the kernel still, but nevertheless, I think this is a step in the right direction.

This function itself should be unsafe too, I just noticed. Let's change that.

src/arch/aarch64/mm/mod.rs

src/arch/x86_64/mm/mod.rs

m-mueller678 · 2025-10-22T14:54:32Z

src/mm/page_range_alloc.rs

+		Ok(Self(range, PhantomData))
+	}
+
+	pub unsafe fn from_raw(range: PageRange) -> Self {


Feels like there should be an into_raw too for symmetry.

Makes sense. I added it. 👍

m-mueller678 · 2025-10-22T14:54:35Z

src/mm/page_range_alloc.rs

+	unsafe fn deallocate(range: PageRange);
+}
+
+pub struct PageRangeBox<A: PageRangeAllocator>(PageRange, PhantomData<A>);


I very much like the idea of PageRangeBox 👍

m-mueller678 · 2025-10-22T14:57:16Z

src/mm/physicalmem.rs

 	InterruptTicketMutex::new(FreeList::new());
 pub static TOTAL_MEMORY: AtomicUsize = AtomicUsize::new(0);

+pub struct FrameAlloc;


I like the idea of having these as methods rather than free standing functions. Both to enable PageRangeBox and to have something natural to implement x86_64's FrameAllocator on.

Co-authored-by: m-mueller678 <[email protected]>

This replaces uses of KERNEL_FREE_LIST with PageAlloc. This replaces uses of PHYSICAL_FREE_LIST with FrameAlloc. Note that this will slow down parts of x86-64 paging right now, since it is not possible to hold a global `FrameAlloc` lock anymore. This means the lock has to be reacquired again and again until we improve the paging code or the `FrameAlloc` code. Co-authored-by: m-mueller678 <[email protected]>

mkroening · 2025-10-23T15:09:13Z

With #2008 merged, this should now be ready too.

mkroening self-assigned this Oct 21, 2025

mkroening force-pushed the page_alloc branch 4 times, most recently from 374c53b to d32f419 Compare October 21, 2025 15:11

github-actions bot reviewed Oct 22, 2025

View reviewed changes

mkroening force-pushed the page_alloc branch from e3a2fde to 6cbf2e3 Compare October 22, 2025 14:15

mkroening mentioned this pull request Oct 22, 2025

fix(mman): don't deallocate PROT_NONE frames #2008

Merged

m-mueller678 suggested changes Oct 22, 2025

View reviewed changes

mkroening and others added 3 commits October 23, 2025 16:46

feat(mm): add PageAlloc, FrameAlloc

e72afef

Co-authored-by: m-mueller678 <[email protected]>

feat(mm): add PageRangeBox, PageBox, FrameBox

0887b57

mkroening force-pushed the page_alloc branch from c771230 to e72afef Compare October 23, 2025 15:07

mkroening marked this pull request as ready for review October 23, 2025 15:09

refactor(x86_64): migrate to PageBox

786d4e9

mkroening force-pushed the page_alloc branch from 22cdfbb to 786d4e9 Compare October 24, 2025 14:17

mkroening added 4 commits October 27, 2025 10:07

refactor(arch): merge init_page_tables into mm::init

82ea5fa

fix(riscv64): make init_page_tables unsafe

adf09f1

fix(mm): make arch::mm::init unsafe

4fbb248

fix(mm): make virtualmem and physicalmem functions unsafe as appropriate

29277d9

mkroening added this pull request to the merge queue Oct 27, 2025

Merged via the queue into main with commit 6019ba4 Oct 27, 2025
16 of 17 checks passed

mkroening deleted the page_alloc branch October 27, 2025 12:47

mkroening mentioned this pull request Oct 27, 2025

Proposal for a new memory management system #1993

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