shmget: make small free numbers reusable.

Change-Id: Ic6670214fa31a309e96794361e3ec2dcc6375f4a
Refs: #1531

kernel/include/syscall.h

@@ -679,4 +679,5 @@ extern int (*linux_clock_gettime)(clockid_t clk_id, struct timespec *tp);
 extern void terminate_host(int pid, struct thread *thread);
 struct sig_pending *getsigpending(struct thread *thread, int delflag);
 int interrupt_from_user(void *regs0);
+extern unsigned long shmid_index[];
 #endif

kernel/shmobj.c

@@ -225,8 +225,6 @@ int shmobj_create_indexed(struct shmid_ds *ds, struct shmobj **objp)
 static void shmobj_destroy(struct shmobj *obj)
 {
 	extern struct shm_info the_shm_info;
-	extern struct list_head kds_free_list;
-	extern int the_maxi;
 	struct shmlock_user *user;
 	size_t size;
 	int npages;
@@ -306,27 +304,13 @@ static void shmobj_destroy(struct shmobj *obj)
 		kfree(obj);
 	}
 	else {
+		int i = obj->index / 64;
+		unsigned long x = 1UL << (obj->index % 64);
+
 		list_del(&obj->chain);
 		--the_shm_info.used_ids;
-
-		list_add(&obj->chain, &kds_free_list);
-		/* For index reuse, release in descending order of index. */
-		for (;;) {
-			struct shmobj *p;
-
-			list_for_each_entry(p, &kds_free_list, chain) {
-				if (p->index == the_maxi) {
-					break;
-				}
-			}
-			if (&p->chain == &kds_free_list) {
-				break;
-			}
-
-			list_del(&p->chain);
-			kfree(p);
-			--the_maxi;
-		}
+		shmid_index[i] &= ~x;
+		kfree(obj);
 	}
 	return;
 }

kernel/syscall.c

@@ -6161,9 +6161,40 @@ struct kshmid_ds {
 	struct list_head chain;
 };
 
-int the_maxi = -1;
+unsigned long shmid_index[512];
+
+static int get_shmid_max_index(void)
+{
+	int i;
+	int index = -1;
+
+	for (i = 511; i >= 0; i--) {
+		if (shmid_index[i]) {
+			index = i * 64 + 63 - __builtin_clzl(shmid_index[i]);
+			break;
+		}
+	}
+	return index;
+}
+
+static int get_shmid_index(void)
+{
+	int index = get_shmid_max_index();
+	int i;
+	unsigned long x;
+
+	for (index = 0;; index++) {
+		i = index / 64;
+		x = 1UL << (index % 64);
+		if (!(shmid_index[i] & x)) {
+			shmid_index[i] |= x;
+			break;
+		}
+	}
+	return index;
+}
+
 LIST_HEAD(kds_list);
-LIST_HEAD(kds_free_list);
 struct shminfo the_shminfo = {
 	.shmmax = 64L * 1024 * 1024 * 1024,
 	.shmmin = 1,
@@ -6384,7 +6415,7 @@ int do_shmget(const key_t key, const size_t size, const int shmflg)
 		return error;
 	}
 
-	obj->index = ++the_maxi;
+	obj->index = get_shmid_index();
 
 	list_add(&obj->chain, &kds_list);
 	++the_shm_info.used_ids;
@@ -6670,7 +6701,7 @@ SYSCALL_DECLARE(shmctl)
 			return error;
 		}
 
-		maxi = the_maxi;
+		maxi = get_shmid_max_index();
 		if (maxi < 0) {
 			maxi = 0;
 		}
@@ -6777,7 +6808,7 @@ SYSCALL_DECLARE(shmctl)
 			return error;
 		}
 
-		maxi = the_maxi;
+		maxi = get_shmid_max_index();
 		if (maxi < 0) {
 			maxi = 0;
 		}