basic layout of allocator

src/allocator.rs

@@ -2,7 +2,30 @@ use std::mem::size_of;
 
 use zerocopy::{AsBytes, FromBytes, Unaligned};
 
-use crate::{Db, FilePointer, Header, PAGE_SIZE, U32};
+use crate::{Db, FilePointer, FileRange, Header, PAGE_SIZE, U32};
+
+enum SlabKind {
+    SplitFreeList,
+    RelativeFreeList,
+    AbsoluteFreeList,
+}
+
+impl SlabKind {
+    fn for_size(size: u32) -> Self {
+        if size == 1 {
+            Self::SplitFreeList
+        } else if size < 8 {
+            Self::RelativeFreeList
+        } else if (size as u64) <= PAGE_SIZE {
+            Self::AbsoluteFreeList
+        } else {
+            panic!("invalid size")
+        }
+    }
+}
+
+// Best bitmap sizes in bytes for a 4096 Byte slab
+// const BITMAP_SIZE: [u32; 8] = [456, 241, 164, 125, 100, 84, 72, 63];
 
 #[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
 #[repr(transparent)]
@@ -22,43 +45,161 @@ impl FreeList {
 #[repr(C)]
 pub struct AllocatorState {
     pub general: FreeList,
-    pub slabs: FilePointer,
+    pub slabs: SlabListPointer,
 }
 
 #[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
 #[repr(C)]
-pub struct PoolListHeader {
-    next: FilePointer,
-    size: U32,
+pub struct SlabListHeader {
+    next: SlabListPointer,
     len: U32,
+    size: U32,
 }
 
-impl PoolListHeader {
-    fn capacity(&self) -> u32 {
-        (self.size.get() - size_of::<PoolListHeader>() as u32) / size_of::<SizedFreeList>() as u32
+#[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
+#[repr(transparent)]
+pub struct SlabListPointer(pub FilePointer);
+
+impl SlabListHeader {
+    pub fn capacity(&self) -> u32 {
+        (self.size.get() - size_of::<SlabListHeader>() as u32) / size_of::<Slab>() as u32
     }
 }
 
-#[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
-#[repr(C)]
-pub struct SizedFreeList {
-    element_size: U32,
-    head: FreeList,
-}
+impl SlabListPointer {
+    pub fn set_next(&self, db: &mut Db, next: SlabListPointer) {
+        db.write(self.0, next);
+    }
 
-impl AllocatorState {
-    pub fn init(&self, db: &mut Db, size: U32) {
+    pub fn set_len(&self, db: &mut Db, len: u32) {
+        db.write(self.0 + size_of::<SlabListPointer>() as u64, U32::from(len));
+    }
+
+    pub fn init(&self, db: &mut Db, size: u32) {
         db.write(
-            self.slabs,
-            PoolListHeader {
-                next: FilePointer::null(),
-                size,
+            self.0,
+            SlabListHeader {
+                next: SlabListPointer(FilePointer::null()),
+                size: size.into(),
                 len: 0.into(),
             },
         );
     }
 
-    fn slabs_mut<'db>(&self, db: &'db mut Db) -> &'db mut PoolListHeader {
-        db.modify(self.slabs)
+    pub fn ptr(&self, db: &Db, i: u32) -> FilePointer {
+        let this: SlabListHeader = db.read(self.0);
+        assert!(i < this.len.get());
+        self.0 + size_of::<SlabListHeader>() as u64 + i as u64 * size_of::<Slab>() as u64
+    }
+
+    pub fn write(&self, db: &mut Db, i: u32, value: Slab) {
+        let ptr = self.ptr(db, i);
+        db.write(ptr, value);
+    }
+
+    pub fn get(&self, db: &Db, i: u32) -> SlabPointer {
+        let ptr = self.ptr(db, i);
+        SlabPointer(ptr)
+    }
+
+    pub fn add(&self, db: &mut Db, slab_size: u32) -> SlabPointer {
+        let this: SlabListHeader = db.read(self.0);
+        let capacity = this.capacity();
+        let SlabListHeader { mut next, len, .. } = this;
+
+        if len.get() >= capacity {
+            if next.0 == FilePointer::null() {
+                next = SlabListPointer(db.add_pages(1));
+                next.init(db, PAGE_SIZE as u32);
+                self.set_next(db, next);
+            }
+
+            return next.add(db, slab_size);
+        }
+
+        let len = len.get();
+        self.set_len(db, len + 1);
+        self.write(
+            db,
+            len,
+            Slab {
+                head: FilePointer::null(),
+                size: slab_size.into(),
+            },
+        );
+
+        SlabPointer(self.ptr(db, len))
+    }
+}
+
+#[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
+#[repr(C)]
+pub struct Slab {
+    head: FilePointer,
+    size: U32,
+}
+
+#[derive(Clone, Copy, FromBytes, AsBytes, Unaligned)]
+#[repr(transparent)]
+pub struct SlabPointer(FilePointer);
+
+impl SlabPointer {
+    pub fn read(&self, db: &Db) -> Slab {
+        db.read(self.0)
+    }
+
+    pub fn get(&self, db: &mut Db) -> FileRange {
+        let Slab { head, size } = self.read(db);
+
+        let size = size.get();
+
+        match SlabKind::for_size(size) {
+            SlabKind::SplitFreeList => todo!(),
+            SlabKind::RelativeFreeList => todo!(),
+            SlabKind::AbsoluteFreeList => {
+                let mut next = head;
+
+                if next == FilePointer::null() {
+                    next = self.allocate_page(db);
+                }
+
+                let new_next = db.read(next);
+
+                self.set_next(db, new_next);
+
+                next.range(size as u64)
+            }
+        }
+    }
+
+    pub fn set_next(&self, db: &mut Db, next: FilePointer) {
+        db.write(self.0, next);
+    }
+
+    pub fn allocate_page(&self, db: &mut Db) -> FilePointer {
+        let Slab { head, size } = self.read(db);
+
+        let size = size.get();
+
+        match SlabKind::for_size(size) {
+            SlabKind::SplitFreeList => todo!(),
+            SlabKind::RelativeFreeList => todo!(),
+            SlabKind::AbsoluteFreeList => {
+                let n = PAGE_SIZE / size as u64;
+
+                let page = db.add_pages(1);
+
+                let mut next = head;
+                for i in (0..n).rev() {
+                    let current = page + i * size as u64;
+                    db.write(current, next);
+                    next = current;
+                }
+
+                self.set_next(db, next);
+
+                next
+            }
+        }
     }
 }

src/atomic_arc.rs

@@ -62,7 +62,7 @@ mod tests {
         let first = atomic_arc.get();
         assert_eq!(*first, 1);
 
-        atomic_arc.swap(Arc::new(2));
+        _ = atomic_arc.swap(Arc::new(2));
 
         assert_eq!(*first, 1);
 

src/lib.rs

@@ -3,7 +3,7 @@ use std::{borrow::BorrowMut, collections::HashMap, fs::File, mem::size_of, ops::
 mod allocator;
 mod atomic_arc;
 
-use allocator::{AllocatorState, FreeList};
+use allocator::{AllocatorState, FreeList, SlabListPointer, SlabPointer};
 use atomic_arc::AtomicArc;
 use memmap::{Mmap, MmapMut};
 use zerocopy::{AsBytes, FromBytes, LayoutVerified, Unaligned, LE};
@@ -75,7 +75,7 @@ impl Default for Header {
             root: FilePointer::null(),
             allocator_state: AllocatorState {
                 general: FreeList::empty(),
-                slabs: FilePointer::page(0) + size_of::<Header>() as u64,
+                slabs: SlabListPointer(FilePointer::page(0) + size_of::<Header>() as u64),
             },
         }
     }
@@ -172,7 +172,12 @@ impl<'t> TransactionHandle<'t> {
 }
 
 impl Db {
-    fn transaction(f: fn(TransactionHandle)) {
+    pub fn add_slab(&mut self, size: u32) -> SlabPointer {
+        let allocator_state = self.header.allocator_state;
+        allocator_state.slabs.add(self, size)
+    }
+
+    fn transaction(f: impl FnOnce(TransactionHandle)) {
         // let handle = TransactionHandle {};
     }
 
@@ -259,12 +264,13 @@ impl Db {
         unsafe { Mmap::map(&self.file) }.unwrap()
     }
 
-    fn add_pages(&mut self, n: u64) {
-        self.file
-            .set_len(self.file.metadata().unwrap().len() + PAGE_SIZE * n)
-            .unwrap();
+    fn add_pages(&mut self, n: u64) -> FilePointer {
+        let len = self.file.metadata().unwrap().len();
+        self.file.set_len(len + PAGE_SIZE * n).unwrap();
 
         self.remap();
+
+        FilePointer::null() + len
     }
 
     pub fn new(file: File) -> Self {
@@ -302,7 +308,7 @@ impl Db {
 
     fn init_allocator(&mut self) {
         let allocator_state = self.header.allocator_state;
-        allocator_state.init(
+        allocator_state.slabs.init(
             self,
             (PAGE_SIZE - size_of::<Header>() as u64).try_into().unwrap(),
         );
@@ -318,7 +324,19 @@ mod tests {
 
     #[test]
     fn it_works() {
-        let db = Db::new(tempfile::tempfile().unwrap());
+        let mut db = Db::new(tempfile::tempfile().unwrap());
+
+        let slab = db.add_slab(16);
+
+        for i in 1..520 {
+            let range = slab.get(&mut db);
+            let start = range.start.0.get();
+            dbg!(start);
+
+            let data = [0; 16].map(|_| i as u8);
+
+            db.write_range(range, data);
+        }
 
         let mut child = std::process::Command::new("hexdump")
             .arg("-C")