kernel: vm: Add virtual memory statistics

Introduce the '/ctl/vm/stat' control file for providing virtual memory
related statistics to userland.

Signed-off-by: Ian Moffett <ian@osmora.org>

6 files changed, 213 insertions, 0 deletions

diff --git a/sys/include/sys/vmstat.h b/sys/include/sys/vmstat.h
new file mode 100644
index 0000000..127bc96
--- /dev/null
+++ b/sys/include/sys/vmstat.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_VMSTAT_H_
+#define _SYS_VMSTAT_H_
+
+#include <sys/types.h>
+
+/*
+ * Virtual memory statistics
+ *
+ * @mem_avail: Available memory in MiB
+ * @mem_used: Allocated memory in MiB
+ */
+struct vm_stat {
+    uint32_t mem_avail;
+    uint32_t mem_used;
+};
+
+#endif  /* !_VM_STAT_H_ */
diff --git a/sys/include/vm/physmem.h b/sys/include/vm/physmem.h
index ae11530..e16bcf9 100644
--- a/sys/include/vm/physmem.h
+++ b/sys/include/vm/physmem.h
@@ -32,6 +32,9 @@
 
 #include <sys/types.h>
 
+uint32_t vm_mem_used(void);
+uint32_t vm_mem_free(void);
+
 void vm_physmem_init(void);
 uintptr_t vm_alloc_frame(size_t count);
 void vm_free_frame(uintptr_t base, size_t count);
diff --git a/sys/include/vm/stat.h b/sys/include/vm/stat.h
new file mode 100644
index 0000000..7e9a4a9
--- /dev/null
+++ b/sys/include/vm/stat.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _VM_STAT_H_
+#define _VM_STAT_H_
+
+#include <sys/types.h>
+#include <sys/vmstat.h>
+
+int vm_stat_get(struct vm_stat *vmstat);
+void vm_stat_init(void);
+
+#endif  /* !_VM_STAT_H_ */
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index 541355a..577b7ec 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -43,6 +43,7 @@
 #include <machine/cpu.h>
 #include <machine/cdefs.h>
 #include <vm/vm.h>
+#include <vm/stat.h>
 #include <string.h>
 
 #define _START_PATH "/usr/sbin/init"
@@ -104,6 +105,9 @@ main(void)
     /* Init the virtual file system */
     vfs_init();
 
+    /* Init vmstats */
+    vm_stat_init();
+
     /* Expose the console to devfs */
     cons_expose();
 
diff --git a/sys/vm/vm_physmem.c b/sys/vm/vm_physmem.c
index 89f9ee6..debec1f 100644
--- a/sys/vm/vm_physmem.c
+++ b/sys/vm/vm_physmem.c
@@ -36,6 +36,10 @@
 #include <vm/vm.h>
 #include <string.h>
 
+#define BYTES_PER_MIB 8388608
+
+static size_t pages_free = 0;
+static size_t pages_used = 0;
 static size_t highest_frame_idx = 0;
 static size_t bitmap_size = 0;
 static size_t bitmap_free_start = 0;
@@ -63,6 +67,7 @@ physmem_populate_bitmap(void)
 
         if (ent->type != LIMINE_MEMMAP_USABLE) {
             /* This memory is not usable */
+            pages_used += ent->length / DEFAULT_PAGESIZE;
             continue;
         }
 
@@ -73,6 +78,8 @@ physmem_populate_bitmap(void)
         for (size_t j = 0; j < ent->length; j += DEFAULT_PAGESIZE) {
             clrbit(bitmap, (ent->base + j) / DEFAULT_PAGESIZE);
         }
+
+        pages_free += ent->length / DEFAULT_PAGESIZE;
     }
 }
 
@@ -203,6 +210,26 @@ vm_free_frame(uintptr_t base, size_t count)
     spinlock_release(&lock);
 }
 
+/*
+ * Return the amount of memory in MiB that is
+ * currently allocated.
+ */
+uint32_t
+vm_mem_used(void)
+{
+    return (pages_used * DEFAULT_PAGESIZE) / BYTES_PER_MIB;
+}
+
+/*
+ * Return the amount of memory in MiB that is
+ * currently free.
+ */
+uint32_t
+vm_mem_free(void)
+{
+    return (pages_free * DEFAULT_PAGESIZE) / BYTES_PER_MIB;
+}
+
 void
 vm_physmem_init(void)
 {
diff --git a/sys/vm/vm_stat.c b/sys/vm/vm_stat.c
new file mode 100644
index 0000000..8cf2fe4
--- /dev/null
+++ b/sys/vm/vm_stat.c
@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <fs/ctlfs.h>
+#include <vm/physmem.h>
+#include <vm/vm.h>
+#include <vm/stat.h>
+#include <string.h>
+
+#include <sys/syslog.h>
+
+static struct ctlops vm_stat_ctl;
+
+/*
+ * ctlfs hook to read the virtual memory
+ * statistics.
+ */
+static int
+vm_stat_read(struct ctlfs_dev *cdp, struct sio_txn *sio)
+{
+    struct vm_stat stat;
+    int error;
+
+    if (sio->len > sizeof(stat)) {
+        sio->len = sizeof(stat);
+    }
+
+    error = vm_stat_get(&stat);
+    if (error < 0) {
+        return error;
+    }
+
+    memcpy(sio->buf, &stat, sio->len);
+    return sio->len;
+}
+
+int
+vm_stat_get(struct vm_stat *vmstat)
+{
+    if (vmstat == NULL) {
+        return -EINVAL;
+    }
+
+    vmstat->mem_avail = vm_mem_free();
+    vmstat->mem_used = vm_mem_used();
+    return 0;
+}
+
+void
+vm_stat_init(void)
+{
+    char devname[] = "vm";
+    struct ctlfs_dev ctl;
+
+    /* Register a stat control file */
+    ctl.mode = 0444;
+    ctlfs_create_node(devname, &ctl);
+    ctl.devname = devname;
+    ctl.ops = &vm_stat_ctl;
+    ctlfs_create_entry("stat", &ctl);
+}
+
+static struct ctlops vm_stat_ctl = {
+    .read = vm_stat_read,
+    .write = NULL
+};