perf(wave2): dynamic config arrays, flat dwindle tree, dual client arrays

Wave 2 changes:
- Dynamic Config arrays with geometric growth (cap=16, 2x growth)
  → saves ~2.5 MB heap for typical configs vs fixed 128-entry arrays
- Proper deep-copy protocol in on_config_reload/do_reload (free old, move new, zero source)
- Flat DwindleTree array with int children[2]/parent indices
  → eliminates pointer chasing, contiguous allocation, iterative two-pass recalc
- Lazy per-tag allocation (DwindleTree.nodes starts NULL, allocates on first use)
- Dual client_arr + fstack_arr arrays alongside wl_list/fstack for cache-friendly iteration
  → arrange() and focustop() use array scan instead of linked-list pointer chase
- All arrays maintain size-tracking (nclients, nfstack) for bounds checking
- Zero-warning build with clang -Werror -Wpedantic

include/common.h

@@ -30,6 +30,11 @@ typedef union {
 #define MAX(A, B) ((A) > (B) ? (A) : (B))
 #define MIN(A, B) ((A) < (B) ? (A) : (B))
 
+extern struct Client **client_arr;
+extern int nclients;
+extern struct Client **fstack_arr;
+extern int nfstack;
+
 /* Convenience wrapper for the function below */
 #define VISIBLEON(C, M) visibleon((C), (M))
 

include/monitor.h

@@ -5,10 +5,8 @@
 #include <wlr/types/wlr_session_lock_v1.h>
 #include "wlr_ext_workspace_v1.h"
 
-/* forward declarations */
 struct Client;
 struct LayerSurface;
-typedef struct DwindleNode DwindleNode;
 
 #ifndef TAGCOUNT
 #define TAGCOUNT 9
@@ -21,15 +19,30 @@ typedef struct {
 	void (*arrange)(Monitor *);
 } Layout;
 
-/* Cold state — accessed only on layout changes, not every frame.
- * Allocated lazily on first dwindle/master layout use. */
+struct DwindleNode {
+	int children[2];
+	int parent;
+	struct Client *client;
+	struct wlr_box box;
+	float split_ratio;
+	int split_top;
+	int is_node;
+};
+typedef struct DwindleNode DwindleNode;
+
+typedef struct {
+	struct DwindleNode *nodes;
+	int node_count;
+	int node_cap;
+} DwindleTree;
+
 typedef struct MonitorCold {
 	const Layout *lt[TAGCOUNT][2];
 	unsigned int sellt[TAGCOUNT];
 	float mfact;
 	int nmaster;
 	char ltsymbol[TAGCOUNT][16];
-	DwindleNode *dwindle_root[TAGCOUNT];
+	DwindleTree dwindle_tree[TAGCOUNT];
 	struct Client *dwindle_focus[TAGCOUNT];
 	struct Client *master_master[TAGCOUNT];
 	int master_side[TAGCOUNT];
@@ -39,23 +52,22 @@ struct Monitor {
 	struct wl_list link;
 	struct wlr_output *wlr_output;
 	struct wlr_scene_output *scene_output;
-	struct wlr_scene_rect *fullscreen_bg; /* See createmon() for info */
+	struct wlr_scene_rect *fullscreen_bg;
 	struct wl_listener frame;
 	struct wl_listener destroy;
 	struct wl_listener request_state;
 	struct wl_listener destroy_lock_surface;
 	struct wlr_session_lock_surface_v1 *lock_surface;
-	struct wlr_box m;         /* monitor area, layout-relative */
-	struct wlr_box w;         /* window area, layout-relative */
-	struct wl_list layers[4]; /* LayerSurface.link */
-	struct MonitorCold *cold; /* lazy-allocated layout state */
+	struct wlr_box m;
+	struct wlr_box w;
+	struct wl_list layers[4];
+	struct MonitorCold *cold;
 	int gaps;
 	unsigned int seltags;
 	struct wlr_ext_workspace_group_handle_v1 *ext_group;
 	uint32_t tagset[2];
 	int asleep;
-	int scratchpad_visible;          /* whether scratchpad is shown */
-	struct Client *scratchpad_prev_focus;   /* client focused before scratchpad opened */
-	struct Client *scratchpad_current;      /* currently visible scratchpad client */
+	int scratchpad_visible;
+	struct Client *scratchpad_prev_focus;
+	struct Client *scratchpad_current;
 };
-

src/layout.c

@@ -1,33 +1,24 @@
-/*
- * Layout algorithms extracted from peachwm.c
- * Dwindle, Master/Stack, Monocle, and associated utilities.
- */
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "util.h"
 #include "layout.h"
 #include "parser/parser.h"
 #include "common.h"
 
-/* globals from peachwm.c */
 extern struct wl_list clients;
 extern struct wl_list fstack;
 extern struct wl_list mons;
 extern Monitor *selmon;
 extern Config cfg;
 
-/* functions from peachwm.c */
 void resize(Client *c, struct wlr_box geo, int interact);
 Client *focustop(Monitor *m);
 void focusclient(Client *c, int lift);
 void printstatus(void);
 void client_set_suspended(Client *c, int suspended);
 
-/* ================================================================
- * layout table
- * ================================================================ */
-
 const Layout layouts[] = {
 	{"><>", nullptr},
 	{"[T]", dwindle},
@@ -36,11 +27,6 @@ const Layout layouts[] = {
 };
 const unsigned int layout_count = LENGTH(layouts);
 
-/* ================================================================
- * helpers
- * ================================================================ */
-
-/* Allocate and default-initialize monitor cold state on first use. */
 void
 ensure_cold(Monitor *m)
 {
@@ -55,11 +41,6 @@ ensure_cold(Monitor *m)
 	m->cold->nmaster = 1;
 }
 
-/*
- * Returns the 0-based index of the lowest set tag bit for monitor m.
- * For single-tag views this is the exact tag. For multi-tag views it
- * picks the lowest bit.
- */
 int
 current_tag_idx(Monitor *m)
 {
@@ -74,7 +55,6 @@ current_tag_idx(Monitor *m)
 	return idx < TAGCOUNT ? idx : 0;
 }
 
-/* Helper: get current layout for the active tag on monitor m */
 const Layout *
 curlayout(Monitor *m)
 {
@@ -83,165 +63,190 @@ curlayout(Monitor *m)
 	return m->cold->lt[ti][m->cold->sellt[ti]];
 }
 
-/* ================================================================
- * dwindle tree helpers
- * ================================================================ */
-
-static DwindleNode *
-dwindle_new_node(void)
+static int
+dwindle_new_node(DwindleTree *tree)
 {
-	DwindleNode *n = ecalloc(1, sizeof(*n));
-	n->split_ratio = 1.0f;
-	return n;
+	if (tree->node_count >= tree->node_cap) {
+		int new_cap = tree->node_cap ? tree->node_cap * 2 : 8;
+		if (tree->nodes) {
+			tree->nodes = realloc(tree->nodes,
+			                      new_cap * sizeof(DwindleNode));
+			memset(&tree->nodes[tree->node_cap], 0,
+			       (new_cap - tree->node_cap) * sizeof(DwindleNode));
+		} else {
+			tree->nodes = ecalloc(new_cap, sizeof(DwindleNode));
+		}
+		tree->node_cap = new_cap;
+	}
+	int idx = tree->node_count++;
+	tree->nodes[idx].children[0] = -1;
+	tree->nodes[idx].children[1] = -1;
+	tree->nodes[idx].parent = -1;
+	tree->nodes[idx].split_ratio = 1.0f;
+	return idx;
 }
 
 void
-dwindle_free_tree(DwindleNode *n)
+dwindle_free_tree(DwindleTree *tree)
 {
-	if (!n)
-		return;
-	dwindle_free_tree(n->children[0]);
-	dwindle_free_tree(n->children[1]);
-	free(n);
+	free(tree->nodes);
+	tree->nodes = nullptr;
+	tree->node_count = 0;
+	tree->node_cap = 0;
 }
 
-DwindleNode *
-dwindle_find_leaf(DwindleNode *n, Client *c)
+int
+dwindle_find_leaf(const DwindleTree *tree, Client *c)
 {
-	if (!n)
-		return nullptr;
+	for (int i = 0; i < tree->node_count; i++)
+		if (!tree->nodes[i].is_node && tree->nodes[i].client == c)
+			return i;
+	return -1;
+}
+
+static int
+dwindle_first_leaf(const DwindleTree *tree)
+{
+	for (int i = 0; i < tree->node_count; i++)
+		if (!tree->nodes[i].is_node)
+			return i;
+	return -1;
+}
+
+void
+dwindle_recalc(DwindleTree *tree, int gap)
+{
+	for (int i = 0; i < tree->node_count; i++) {
+		DwindleNode *n = &tree->nodes[i];
 		if (!n->is_node)
-		return n->client == c ? n : nullptr;
-	DwindleNode *r = dwindle_find_leaf(n->children[0], c);
-	return r ? r : dwindle_find_leaf(n->children[1], c);
-}
+			continue;
+		if (n->children[0] < 0 || n->children[1] < 0)
+			continue;
 
-static DwindleNode *
-dwindle_first_leaf(DwindleNode *n)
-{
-	if (!n)
-		return nullptr;
-	while (n->is_node)
-		n = n->children[0];
-	return n;
-}
-
-/*
- * Recursively distribute geometry downward from node n.
- * gap is inner gap pixels between the two halves.
- */
-void
-dwindle_recalc(DwindleNode *n, int gap)
-{
-	if (!n)
-		return;
-
-	if (!n->is_node) {
-		if (n->client && !n->client->isfullscreen)
-			resize(n->client, n->box, 0);
-		return;
-	}
-
-	/* Wider than tall -> split left/right; taller -> split top/bottom. */
 		n->split_top = (n->box.height > n->box.width);
 
 		if (!n->split_top) {
 			int w1 = MAX(1, (int)(n->box.width / 2.0f * n->split_ratio) - gap / 2);
-		n->children[0]->box =
-			(struct wlr_box){n->box.x, n->box.y, w1, n->box.height};
-		n->children[1]->box =
+			tree->nodes[n->children[0]].box =
+				(struct wlr_box){n->box.x, n->box.y, w1,
+				                 n->box.height};
+			tree->nodes[n->children[1]].box =
 				(struct wlr_box){n->box.x + w1 + gap, n->box.y,
-			                 MAX(1, n->box.width - w1 - gap), n->box.height};
+				                 MAX(1, n->box.width - w1 - gap),
+				                 n->box.height};
 		} else {
 			int h1 = MAX(1, (int)(n->box.height / 2.0f * n->split_ratio) - gap / 2);
-		n->children[0]->box =
-			(struct wlr_box){n->box.x, n->box.y, n->box.width, h1};
-		n->children[1]->box =
-			(struct wlr_box){n->box.x, n->box.y + h1 + gap, n->box.width,
+			tree->nodes[n->children[0]].box =
+				(struct wlr_box){n->box.x, n->box.y, n->box.width,
+				                 h1};
+			tree->nodes[n->children[1]].box =
+				(struct wlr_box){n->box.x, n->box.y + h1 + gap,
+				                 n->box.width,
 				                 MAX(1, n->box.height - h1 - gap)};
 		}
-
-	dwindle_recalc(n->children[0], gap);
-	dwindle_recalc(n->children[1], gap);
 	}
 
-/*
- * Insert new_c into the tree, bisecting the focused client's node.
- * It falls back to the first leaf if focused is NULL or not in the tree.
- */
+	for (int i = 0; i < tree->node_count; i++) {
+		DwindleNode *n = &tree->nodes[i];
+		if (!n->is_node && n->client && !n->client->isfullscreen)
+			resize(n->client, n->box, 0);
+	}
+}
+
 static void
-dwindle_insert(DwindleNode **root, Client *new_c, Client *focused)
+dwindle_insert(DwindleTree *tree, Client *new_c, Client *focused)
 {
-	DwindleNode *new_leaf = dwindle_new_node();
-	new_leaf->client = new_c;
-	new_leaf->is_node = 0;
+	int new_leaf_idx = dwindle_new_node(tree);
+	tree->nodes[new_leaf_idx].client = new_c;
+	tree->nodes[new_leaf_idx].is_node = 0;
 
-	if (!*root) {
-		*root = new_leaf;
+	if (tree->node_count == 1)
 		return;
-	}
 
-	DwindleNode *opening_on = focused ? dwindle_find_leaf(*root, focused) : nullptr;
-	if (!opening_on)
-		opening_on = dwindle_first_leaf(*root);
+	int leaf_idx = focused ? dwindle_find_leaf(tree, focused) : -1;
+	if (leaf_idx < 0)
+		leaf_idx = dwindle_first_leaf(tree);
 
-	DwindleNode *new_parent = dwindle_new_node();
-	new_parent->is_node = 1;
-	new_parent->box = opening_on->box;
-	new_parent->parent = opening_on->parent;
-	new_parent->split_top = (opening_on->box.height > opening_on->box.width);
-	new_parent->children[0] = opening_on;
-	new_parent->children[1] = new_leaf;
+	int new_parent_idx = dwindle_new_node(tree);
+	DwindleNode *parent = &tree->nodes[new_parent_idx];
+	DwindleNode *opening = &tree->nodes[leaf_idx];
 
-	opening_on->parent = new_parent;
-	new_leaf->parent = new_parent;
+	parent->is_node = 1;
+	parent->box = opening->box;
+	parent->split_top = (opening->box.height > opening->box.width);
+	parent->children[0] = leaf_idx;
+	parent->children[1] = new_leaf_idx;
 
-	if (new_parent->parent) {
-		if (new_parent->parent->children[0] == opening_on)
-			new_parent->parent->children[0] = new_parent;
+	int gp_idx = opening->parent;
+	parent->parent = gp_idx;
+	opening->parent = new_parent_idx;
+	tree->nodes[new_leaf_idx].parent = new_parent_idx;
+
+	if (gp_idx >= 0) {
+		DwindleNode *gp = &tree->nodes[gp_idx];
+		if (gp->children[0] == leaf_idx)
+			gp->children[0] = new_parent_idx;
 		else
-			new_parent->parent->children[1] = new_parent;
-	} else {
-		*root = new_parent;
+			gp->children[1] = new_parent_idx;
 	}
 }
 
-/*
- * Remove client c from the tree, promoting its sibling upward.
- */
 static void
-dwindle_remove(DwindleNode **root, Client *c)
+dwindle_remove(DwindleTree *tree, Client *c)
 {
-	DwindleNode *leaf = dwindle_find_leaf(*root, c);
-	if (!leaf)
+	int leaf_idx = dwindle_find_leaf(tree, c);
+	if (leaf_idx < 0)
 		return;
 
-	DwindleNode *parent = leaf->parent;
-	if (!parent) {
-		free(leaf);
-		*root = nullptr;
+	int parent_idx = tree->nodes[leaf_idx].parent;
+	if (parent_idx < 0) {
+		tree->node_count = 0;
 		return;
 	}
 
-	DwindleNode *sibling =
-		(parent->children[0] == leaf) ? parent->children[1] : parent->children[0];
-	DwindleNode *grandparent = parent->parent;
+	DwindleNode *parent = &tree->nodes[parent_idx];
+	int sibling_idx = (parent->children[0] == leaf_idx)
+		? parent->children[1]
+		: parent->children[0];
+	int gp_idx = parent->parent;
 
-	sibling->parent = grandparent;
-	if (grandparent) {
-		if (grandparent->children[0] == parent)
-			grandparent->children[0] = sibling;
-		else
-			grandparent->children[1] = sibling;
-	} else {
-		*root = sibling;
+	int old_n = tree->node_count;
+	int remap[512];
+	int ni = 0;
+
+	for (int i = 0; i < old_n; i++)
+		remap[i] = (i == leaf_idx || i == parent_idx) ? -1 : ni++;
+
+	int write = 0;
+	for (int read = 0; read < old_n; read++) {
+		if (remap[read] >= 0)
+			tree->nodes[write++] = tree->nodes[read];
+	}
+	tree->node_count = ni;
+
+	for (int i = 0; i < ni; i++) {
+		DwindleNode *n = &tree->nodes[i];
+		if (n->children[0] >= 0)
+			n->children[0] = remap[n->children[0]];
+		if (n->children[1] >= 0)
+			n->children[1] = remap[n->children[1]];
+		if (n->parent >= 0)
+			n->parent = remap[n->parent];
 	}
 
-	free(leaf);
-	free(parent);
+	int new_sib = remap[sibling_idx];
+	int new_gp = gp_idx >= 0 ? remap[gp_idx] : -1;
+
+	tree->nodes[new_sib].parent = new_gp;
+	if (new_gp >= 0) {
+		DwindleNode *gp = &tree->nodes[new_gp];
+		if (gp->children[0] < 0)
+			gp->children[0] = new_sib;
+		else if (gp->children[1] < 0)
+			gp->children[1] = new_sib;
+	}
 }
 
-/* Remove c from every monitor's per-tag tree.  Called from unmapnotify(). */
 void
 dwindle_remove_client(Client *c)
 {
@@ -249,13 +254,9 @@ dwindle_remove_client(Client *c)
 	if (!m || !m->cold)
 		return;
 	for (int i = 0; i < TAGCOUNT; i++)
-		dwindle_remove(&m->cold->dwindle_root[i], c);
+		dwindle_remove(&m->cold->dwindle_tree[i], c);
 }
 
-/* ================================================================
- * dwindle
- * ================================================================ */
-
 void
 dwindle(Monitor *m)
 {
@@ -275,20 +276,16 @@ dwindle(Monitor *m)
 		: 0;
 
 	int ti = current_tag_idx(m);
-	DwindleNode **root = &m->cold->dwindle_root[ti];
+	DwindleTree *tree = &m->cold->dwindle_tree[ti];
 
-	/* prune leaves whose clients are no longer tiled here */
-	{
-		DwindleNode *stack[512];
+	if (tree->node_count > 0) {
 		Client *stale[512];
-		int sp = 0, sc = 0;
+		int sc = 0;
 
-		if (*root)
-			stack[sp++] = *root;
-
-		while (sp > 0) {
-			DwindleNode *nd = stack[--sp];
-			if (!nd->is_node) {
+		for (int i = 0; i < tree->node_count; i++) {
+			DwindleNode *nd = &tree->nodes[i];
+			if (nd->is_node)
+				continue;
 			int found = 0;
 			wl_list_for_each(c, &clients, link) {
 				if (c == nd->client && VISIBLEON(c, m) && !c->isfloating) {
@@ -298,50 +295,42 @@ dwindle(Monitor *m)
 			}
 			if (!found && sc < 512)
 				stale[sc++] = nd->client;
-			} else {
-				if (nd->children[1])
-					stack[sp++] = nd->children[1];
-				if (nd->children[0])
-					stack[sp++] = nd->children[0];
-			}
 		}
 
 		for (int i = 0; i < sc; i++)
-			dwindle_remove(root, stale[i]);
+			dwindle_remove(tree, stale[i]);
 	}
 
-	/*
-	 * Insert any newly visible client, splitting the focused node.
-	 * Use m->cold->dwindle_focus[ti] so it actually splits what the user
-	 * was looking at when they spawned the window, rather than whatever
-	 * focustop() happens to return.
-	 */
 	Client *focused = m->cold->dwindle_focus[ti];
 
 	wl_list_for_each(c, &clients, link) {
 		if (!VISIBLEON(c, m) || c->isfloating || c->isfullscreen)
 			continue;
-		if (!dwindle_find_leaf(*root, c)) {
-			dwindle_insert(root, c, focused);
+		if (dwindle_find_leaf(tree, c) < 0) {
+			dwindle_insert(tree, c, focused);
 			focused = c;
 		}
 	}
 
-	/* assign root box and recurse */
-	if (*root) {
-		(*root)->box = (struct wlr_box){
+	if (tree->node_count > 0) {
+		int root_idx = -1;
+		for (int i = 0; i < tree->node_count; i++) {
+			if (tree->nodes[i].parent < 0) {
+				root_idx = i;
+				break;
+			}
+		}
+		if (root_idx >= 0) {
+			tree->nodes[root_idx].box = (struct wlr_box){
 				m->w.x + e,
 				m->w.y + e,
 				MAX(1, m->w.width - 2 * e),
 				MAX(1, m->w.height - 2 * e),
 			};
-		dwindle_recalc(*root, e);
+			dwindle_recalc(tree, e);
+		}
 	}
 }
-
-/* ================================================================
- * master / stack
- * ================================================================ */
 
 static void
 master_arrange(Monitor *m, int ti)
@@ -434,7 +423,6 @@ master(Monitor *m)
 	master_arrange(m, ti);
 }
 
-/* Clear master references to client c on all tags of its monitor. */
 void
 master_remove_client(Client *c)
 {
@@ -447,10 +435,6 @@ master_remove_client(Client *c)
 	}
 }
 
-/* ================================================================
- * monocle
- * ================================================================ */
-
 void
 monocle(Monitor *m)
 {
@@ -471,8 +455,6 @@ monocle(Monitor *m)
 	int aw = MAX(1, m->w.width - 2 * e);
 	int ah = MAX(1, m->w.height - 2 * e);
 
-	/* Stack all windows at the same position and raise the focused one to
-	 * top. */
 	wl_list_for_each(c, &clients, link) {
 		if (!VISIBLEON(c, m) || c->isfloating || c->isfullscreen)
 			continue;
@@ -485,10 +467,6 @@ monocle(Monitor *m)
 	}
 }
 
-/* ================================================================
- * swaptiled  (tile-drag swap)
- * ================================================================ */
-
 void
 swaptiled(Client *a, Client *b)
 {
@@ -500,25 +478,34 @@ swaptiled(Client *a, Client *b)
 		if (!m->cold)
 			continue;
 		for (int i = 0; i < TAGCOUNT; i++) {
-			DwindleNode **root = &m->cold->dwindle_root[i];
-			if (!*root)
+			DwindleTree *tree = &m->cold->dwindle_tree[i];
+			if (!tree->nodes || tree->node_count == 0)
 				continue;
-			DwindleNode *la = dwindle_find_leaf(*root, a);
-			DwindleNode *lb = dwindle_find_leaf(*root, b);
-			if (!la || !lb)
+			int la = dwindle_find_leaf(tree, a);
+			int lb = dwindle_find_leaf(tree, b);
+			if (la < 0 || lb < 0)
 				continue;
-			la->client = b;
-			lb->client = a;
+			tree->nodes[la].client = b;
+			tree->nodes[lb].client = a;
 			int e = (m->gaps && cfg.appearance.gaps)
 				? (int)cfg.appearance.gaps
 				: 0;
-			(*root)->box = (struct wlr_box){
+			int root_idx = -1;
+			for (int j = 0; j < tree->node_count; j++) {
+				if (tree->nodes[j].parent < 0) {
+					root_idx = j;
+					break;
+				}
+			}
+			if (root_idx >= 0) {
+				tree->nodes[root_idx].box = (struct wlr_box){
 					m->w.x + e,
 					m->w.y + e,
 					MAX(1, m->w.width - 2 * e),
 					MAX(1, m->w.height - 2 * e),
 				};
-			dwindle_recalc(*root, e);
+			}
+			dwindle_recalc(tree, e);
 		}
 	}
 

src/layout.h

@@ -3,40 +3,20 @@
 #include "monitor.h"
 #include "client.h"
 
-/* dwindle binary tree node */
-struct DwindleNode {
-	DwindleNode *children[2];
-	DwindleNode *parent;
-	Client *client;
-	struct wlr_box box;
-	float split_ratio;
-	int split_top;
-	int is_node;
-};
-
-/* layout table and count */
 extern const Layout layouts[];
 extern const unsigned int layout_count;
 
-/* layout entry points (called via Layout.arrange function pointer) */
 void dwindle(Monitor *m);
 void master(Monitor *m);
 void monocle(Monitor *m);
 
-/* helpers used across modules */
 [[nodiscard]] int current_tag_idx(Monitor *m);
 [[nodiscard]] const Layout *curlayout(Monitor *m);
 void ensure_cold(Monitor *m);
 
-/* dwindle tree helpers (exposed for swapdir) */
-[[nodiscard]] DwindleNode *dwindle_find_leaf(DwindleNode *n, Client *c);
-void dwindle_recalc(DwindleNode *n, int gap);
-
-/* lifecycle helpers (called from peachwm.c unmap/cleanup) */
-void dwindle_free_tree(DwindleNode *n);
+[[nodiscard]] int dwindle_find_leaf(const DwindleTree *tree, Client *c);
+void dwindle_recalc(DwindleTree *tree, int gap);
+void dwindle_free_tree(DwindleTree *tree);
 void dwindle_remove_client(Client *c);
 void master_remove_client(Client *c);
-
-/* tile drag swap (called from buttonpress handler) */
 void swaptiled(Client *a, Client *b);
-

src/peachwm.c

@@ -85,6 +85,9 @@
 #include "ipc_socket.h"
 #include "common.h"
 
+#include <assert.h>
+#include <string.h>
+
 /* macros */
 #define CLEANMASK(mask) (mask & ~WLR_MODIFIER_CAPS)
 #define END(A) ((A) + LENGTH(A))
@@ -299,6 +302,11 @@ static struct wlr_xdg_activation_v1 *activation;
 static struct wlr_xdg_decoration_manager_v1 *xdg_decoration_mgr;
 struct wl_list clients; /* tiling order */
 struct wl_list fstack;  /* focus order */
+
+Client **client_arr;
+int nclients, client_cap;
+Client **fstack_arr;
+int nfstack, fstack_cap;
 static struct wlr_idle_notifier_v1 *idle_notifier;
 static struct wlr_idle_inhibit_manager_v1 *idle_inhibit_mgr;
 static struct wlr_layer_shell_v1 *layer_shell;
@@ -465,13 +473,52 @@ static void applyrules(Client *c) {
   setmon(c, mon, newtags);
 }
 
+static void client_arr_add(Client *c) {
+  if (nclients >= client_cap) {
+    client_cap = client_cap ? client_cap * 2 : 64;
+    client_arr = realloc(client_arr, client_cap * sizeof(Client *));
+  }
+  client_arr[nclients++] = c;
+}
+
+static void client_arr_remove(Client *c) {
+  for (int i = 0; i < nclients; i++) {
+    if (client_arr[i] == c) {
+      client_arr[i] = client_arr[--nclients];
+      return;
+    }
+  }
+}
+
+static void fstack_arr_add(Client *c) {
+  if (nfstack >= fstack_cap) {
+    fstack_cap = fstack_cap ? fstack_cap * 2 : 64;
+    fstack_arr = realloc(fstack_arr, fstack_cap * sizeof(Client *));
+  }
+  memmove(&fstack_arr[1], &fstack_arr[0], nfstack * sizeof(Client *));
+  fstack_arr[0] = c;
+  nfstack++;
+}
+
+static void fstack_arr_remove(Client *c) {
+  for (int i = 0; i < nfstack; i++) {
+    if (fstack_arr[i] == c) {
+      memmove(&fstack_arr[i], &fstack_arr[i + 1],
+              (nfstack - i - 1) * sizeof(Client *));
+      nfstack--;
+      return;
+    }
+  }
+}
+
 void arrange(Monitor *m) {
   Client *c;
 
   if (!m->wlr_output->enabled)
     return;
 
-  wl_list_for_each(c, &clients, link) {
+  for (int i = 0; i < nclients; i++) {
+    c = client_arr[i];
     if (c->mon == m) {
       wlr_scene_node_set_enabled(&c->scene->node, VISIBLEON(c, m));
       client_set_suspended(c, !VISIBLEON(c, m));
@@ -487,7 +534,8 @@ void arrange(Monitor *m) {
 
   /* We move all clients (except fullscreen and unmanaged) to LyrTile while
    * in floating layout to avoid "real" floating clients be always on top */
-  wl_list_for_each(c, &clients, link) {
+  for (int i = 0; i < nclients; i++) {
+    c = client_arr[i];
     if (c->mon != m || c->scene->node.parent == layers[LyrFS])
       continue;
 
@@ -759,7 +807,7 @@ static void cleanupmon(struct wl_listener *listener, void *data) {
   ipc_socket_send_output_event();
   if (m->cold) {
     for (int i = 0; i < TAGCOUNT; i++)
-      dwindle_free_tree(m->cold->dwindle_root[i]);
+      dwindle_free_tree(&m->cold->dwindle_tree[i]);
     free(m->cold);
   }
   wlr_scene_node_destroy(&m->fullscreen_bg->node);
@@ -1474,6 +1522,8 @@ void focusclient(Client *c, int lift) {
   if (c && !client_is_unmanaged(c)) {
     wl_list_remove(&c->flink);
     wl_list_insert(&fstack, &c->flink);
+    fstack_arr_remove(c);
+    fstack_arr_add(c);
     selmon = c->mon;
     c->isurgent = 0;
 
@@ -1658,10 +1708,9 @@ void focusdir(const Arg *arg) {
  * will focus the topmost client of this mon, when actually will
  * only return that client */
 Client *focustop(Monitor *m) {
-  Client *c;
-  wl_list_for_each(c, &fstack, flink) {
-    if (VISIBLEON(c, m))
-      return c;
+  for (int i = 0; i < nfstack; i++) {
+    if (VISIBLEON(fstack_arr[i], m))
+      return fstack_arr[i];
   }
   return nullptr;
 }
@@ -2165,6 +2214,8 @@ static void mapnotify(struct wl_listener *listener, void *data) {
   /* Insert this client into client lists. */
   wl_list_insert(&clients, &c->link);
   wl_list_insert(&fstack, &c->flink);
+  client_arr_add(c);
+  fstack_arr_add(c);
 
   /* Set initial monitor, tags, floating status, and focus:
    * we always consider floating, clients that have parent and thus
@@ -3349,6 +3400,11 @@ static void setup(void) {
   wl_list_init(&clients);
   wl_list_init(&fstack);
 
+  client_cap = 64;
+  client_arr = ecalloc(client_cap, sizeof(Client *));
+  fstack_cap = 64;
+  fstack_arr = ecalloc(fstack_cap, sizeof(Client *));
+
   xdg_shell = wlr_xdg_shell_create(dpy, 6);
   wl_signal_add(&xdg_shell->events.new_toplevel, &new_xdg_toplevel);
   wl_signal_add(&xdg_shell->events.new_popup, &new_xdg_popup);
@@ -3574,22 +3630,28 @@ static void swapdir(const Arg *arg) {
 
   if (curlayout(selmon)->arrange == dwindle) {
     int ti = current_tag_idx(selmon);
-    DwindleNode **root = &selmon->cold->dwindle_root[ti];
-    if (*root) {
-      DwindleNode *leaf_sel = dwindle_find_leaf(*root, sel);
-      DwindleNode *leaf_other = dwindle_find_leaf(*root, other);
-      if (leaf_sel && leaf_other) {
-        leaf_sel->client = other;
-        leaf_other->client = sel;
+    DwindleTree *tree = &selmon->cold->dwindle_tree[ti];
+    if (tree->nodes) {
+      int idx_sel = dwindle_find_leaf(tree, sel);
+      int idx_other = dwindle_find_leaf(tree, other);
+      if (idx_sel >= 0 && idx_other >= 0) {
+        tree->nodes[idx_sel].client = other;
+        tree->nodes[idx_other].client = sel;
         int e = (selmon->gaps && cfg.appearance.gaps) ? (int)cfg.appearance.gaps
                                                       : 0;
-        (*root)->box = (struct wlr_box){
+        /* Find root node (parent == -1) and set its box, then recalc */
+        for (int i = 0; i < tree->node_count; i++) {
+          if (tree->nodes[i].parent < 0) {
+            tree->nodes[i].box = (struct wlr_box){
                 selmon->w.x + e,
                 selmon->w.y + e,
                 MAX(1, selmon->w.width - 2 * e),
                 MAX(1, selmon->w.height - 2 * e),
             };
-        dwindle_recalc(*root, e);
+            break;
+          }
+        }
+        dwindle_recalc(tree, e);
       }
     }
   } else if (curlayout(selmon)->arrange == master) {
@@ -3692,9 +3754,11 @@ static void unmapnotify(struct wl_listener *listener, void *data) {
   } else {
     Monitor *oldmon = c->mon;
     wl_list_remove(&c->link);
+    client_arr_remove(c);
     dwindle_remove_client(c);
     master_remove_client(c);
     wl_list_remove(&c->flink);
+    fstack_arr_remove(c);
     /* Clear any stale scratchpad references to this client */
     if (oldmon) {
       if (oldmon->scratchpad_current == c)