mm: more aggressive reclamation

src/mm/balance.zig

@@ -30,18 +30,52 @@ pub fn init() void {
     ke.sched.enqueue(&td.kern);
 }
 
+fn reap_stacks() void {
+    if (ke.thread.stack_cache_update()) |lst| {
+        // Reap all the excess stacks.
+        var entry: ?*ke.Stack = lst;
+
+        while (entry != null) {
+            const next = entry.?.next;
+            mm.heap.free(
+                (@intFromPtr(entry) + @sizeOf(ke.Stack)) -
+                    ps.thread.kernel_thread_stack_size,
+                ps.thread.kernel_thread_stack_size,
+            );
+            entry = next;
+        }
+    }
+}
+
 fn balance_manager(_: ?*anyopaque) void {
-    while (true) {
+    const low_memory = 0;
+    const timeout = 1;
+
     var timer: ke.Timer = undefined;
     timer.init();
+
+    var which: usize = timeout;
+
+    while (true) {
+        if (which == timeout) {
             ke.timer.set(
                 &timer,
                 .from(r.Milliseconds.init(balance_interval.load())),
                 .{},
             );
+        }
 
-        _ = ke.wait.wait_one(&timer.hdr, "balmgr", .{}) catch unreachable;
+        which = ke.wait.wait_any(&.{
+            &mmp.phys.low_memory_event.hdr,
+            &timer.hdr,
+        }, "balmgr", .{}) catch
+            unreachable;
 
+        if (which == low_memory) {
+            reap_stacks();
+            mm.zone.drain();
+            mmp.phys.low_memory_event.reset();
+        } else if (which == timeout) {
             stack_reap_time -= 1;
             zone_update_time -= 1;
 
@@ -53,18 +87,7 @@ fn balance_manager(_: ?*anyopaque) void {
             if (stack_reap_time == 0) {
                 stack_reap_time = stack_reap_interval;
 
-            if (ke.thread.stack_cache_update()) |lst| {
+                reap_stacks();
-                // Reap all the excess stacks.
-                var entry: ?*ke.Stack = lst;
-
-                while (entry != null) {
-                    const next = entry.?.next;
-                    mm.heap.free(
-                        (@intFromPtr(entry) + @sizeOf(ke.Stack)) - ps.thread.kernel_thread_stack_size,
-                        ps.thread.kernel_thread_stack_size,
-                    );
-                    entry = next;
-                }
             }
         }
     }

src/mm/phys.zig

@@ -17,6 +17,8 @@ pub var min_memory_threshold: usize = 0;
 pub var low_memory_threshold: usize = 0;
 /// Threshold at which reclamation stops.
 pub var high_memory_threshold: usize = 0;
+/// Event triggered when memory is low.
+pub var low_memory_event: ke.Event = undefined;
 
 var memory_map: *r.BootInfo.MemMap = undefined;
 var early_allocs: usize = 0;
@@ -71,6 +73,10 @@ pub fn alloc() r.PAddr {
     _ = usable_memory.fetchSub(mm.page_size, .monotonic);
     free_pages -= 1;
 
+    if (free_pages < min_memory_threshold) {
+        low_memory_event.signal();
+    }
+
     const elem: *mm.PageFree = @fieldParentPtr("link", head);
     const page: *mm.Page = @ptrCast(elem);
     const phys_addr = mm.pfn_to_page(mm.struct_page_to_pfn(page));
@@ -97,6 +103,10 @@ pub fn alloc_opts(opts: struct { policy: mm.WaitPolicy }) ?r.PAddr {
     _ = usable_memory.fetchSub(mm.page_size, .monotonic);
     free_pages -= 1;
 
+    if (free_pages < min_memory_threshold) {
+        low_memory_event.signal();
+    }
+
     const elem: *mm.PageFree = @fieldParentPtr("link", head);
     const page: *mm.Page = @ptrCast(elem);
     const phys_addr = mm.pfn_to_page(mm.struct_page_to_pfn(page));
@@ -144,6 +154,7 @@ pub fn init() linksection(r.init) void {
     memory_map = &r.boot_info.memory_map;
     free_list.init();
     free_page_event.init(.Notification);
+    low_memory_event.init(.Notification);
 
     var total_usable_memory: usize = memory_map.loader_memory_used;
     log.info("physical memory map:", .{});