perf(kernel): linked cap tree, translate-based page lookup, next-fit frames/heap, targeted dequeue; host benches

crates/domain/src/memory/frame/mod.rs

@@ -50,6 +50,8 @@ pub struct FrameTable<const N: usize = MAX_FRAMES> {
     total: usize,
     frames: [Option<FrameUse>; N],
     free: usize,
+    /// Where the next allocation starts looking: just past the last one.
+    cursor: usize,
 }
 
 impl<const N: usize> FrameTable<N> {
@@ -60,6 +62,7 @@ impl<const N: usize> FrameTable<N> {
             total,
             frames: [None; N],
             free: total,
+            cursor: 0,
         }
     }
 
@@ -101,14 +104,21 @@ impl<const N: usize> FrameTable<N> {
         self.frames.get(self.index_of(pa)?)?.as_ref()
     }
 
+    /// Next-fit: searches from just past the previous allocation and wraps
+    /// once, so a run of allocations costs O(1) each instead of rescanning
+    /// the allocated prefix every time.
     pub fn alloc(&mut self, usage: FrameUse) -> Option<PhysicalAddress> {
-        let (idx, slot) = self
-            .live_mut()
-            .iter_mut()
-            .enumerate()
-            .find(|(_, f)| f.is_none())?;
-        *slot = Some(usage);
+        if self.free == 0 {
+            return None;
+        }
+        let total = self.total;
+        let start = self.cursor.min(total);
+        let idx = (start..total)
+            .chain(0..start)
+            .find(|&i| self.frames.get(i).is_some_and(Option::is_none))?;
+        *self.frames.get_mut(idx)? = Some(usage);
         self.free -= 1;
+        self.cursor = idx + 1;
         Some(self.address_of(idx))
     }
 
@@ -168,6 +178,29 @@ impl<const N: usize> FrameTable<N> {
     }
 
     /// The frame mapped at `va` in `owner`, if `owner` holds it as a user page.
+    /// The perms of the frame at `pa` if it is `owner`'s user page at
+    /// `va`; `None` for any other frame. O(1): the caller supplies the
+    /// frame, this only confirms it.
+    pub fn user_at(
+        &self,
+        pa: PhysicalAddress,
+        owner: ProcessId,
+        va: VirtualAddress,
+    ) -> Option<PagePerms> {
+        let page = u32::try_from(va.raw() / PAGE_SIZE).ok()?;
+        if !va.raw().is_multiple_of(PAGE_SIZE) {
+            return None;
+        }
+        match self.get(pa)? {
+            FrameUse::User {
+                owner: o,
+                page: p,
+                perms,
+            } if *o == owner && *p == page => Some(*perms),
+            _ => None,
+        }
+    }
+
     pub fn find_user(
         &self,
         owner: ProcessId,