Initial commit

src/bump_allocator.rs

@@ -0,0 +1,120 @@
+use std::{
+    sync::{LazyLock, Mutex},
+    usize,
+};
+
+use libc::{c_char, c_void, ftruncate, memfd_create, mmap, MAP_SHARED, PROT_READ, PROT_WRITE};
+
+pub(crate) const MEMFD_INITIAL_SIZE: usize = 1024 * 1024 * 4;
+const MMAP_SIZE: usize = 1024 * 1024 * 1024;
+
+pub(crate) static BUMP_ALLOCATOR: LazyLock<Mutex<BumpAllocator>> =
+    LazyLock::new(|| unsafe { Mutex::new(BumpAllocator::new()) });
+
+pub struct BumpAllocator {
+    start_of_mem: *mut u8,
+    head: *mut u8,
+    end_of_mem: *mut u8,
+    number_of_allocated_chunks: usize,
+    backing_fd: i32,
+    fd_size: usize,
+}
+
+unsafe impl Send for BumpAllocator {}
+
+impl BumpAllocator {
+    unsafe fn new() -> Self {
+        assert!(MMAP_SIZE >= MEMFD_INITIAL_SIZE);
+
+        let data_fd = memfd_create("data\x00".as_ptr() as *const c_char, 0);
+
+        assert!(data_fd > 0);
+
+        assert_eq!(ftruncate(data_fd, MEMFD_INITIAL_SIZE as i64), 0);
+
+        let start_of_mem = mmap(
+            0 as *mut c_void,
+            MMAP_SIZE,
+            PROT_READ | PROT_WRITE,
+            MAP_SHARED,
+            data_fd,
+            0,
+        ) as *mut u8;
+
+        assert_ne!(start_of_mem, 0 as *mut u8);
+
+        let end_of_mem = start_of_mem.byte_add(MEMFD_INITIAL_SIZE);
+
+        BumpAllocator {
+            start_of_mem,
+            head: start_of_mem,
+            end_of_mem,
+            number_of_allocated_chunks: 0,
+            backing_fd: data_fd,
+            fd_size: MEMFD_INITIAL_SIZE,
+        }
+    }
+
+    pub unsafe fn alloc(&mut self, size: usize) -> Option<*mut u8> {
+        let new_head = self.head.byte_add(size);
+
+        if new_head > self.end_of_mem {
+            if self.end_of_mem.byte_add(self.fd_size) < self.start_of_mem.byte_add(MMAP_SIZE) {
+                assert_eq!(ftruncate(self.backing_fd, (self.fd_size * 2) as i64), 0);
+                self.fd_size *= 2;
+            } else {
+                return None;
+            }
+        }
+
+        let ret = Some(self.head);
+
+        self.head = new_head;
+        self.number_of_allocated_chunks += 1;
+
+        ret
+    }
+
+    pub fn dealloc(&mut self) {
+        self.number_of_allocated_chunks -= 1;
+
+        if self.number_of_allocated_chunks == 0 {
+            self.head = self.start_of_mem;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    extern crate test;
+
+    use core::slice;
+    use test::Bencher;
+
+    use super::BUMP_ALLOCATOR;
+
+    #[test]
+    fn test() {
+        let mut allocator = BUMP_ALLOCATOR.lock().unwrap();
+
+        unsafe {
+            let x = allocator.alloc(10).unwrap();
+            let x = slice::from_raw_parts_mut(x, 10);
+            x[0] = 1;
+            assert_eq!(x[0], 1);
+        }
+    }
+
+    #[bench]
+    fn bench(b: &mut Bencher) {
+        let mut allocator = BUMP_ALLOCATOR.lock().unwrap();
+
+        b.iter(|| unsafe {
+            let x = allocator.alloc(10).unwrap();
+            let x = slice::from_raw_parts_mut(x, 10);
+            x[0] = 1;
+            assert_eq!(x[0], 1);
+            allocator.dealloc();
+        });
+    }
+}