[LibOS] Support /sys/devices/system/node/nodeX/meminfo files

This commit adds basic support for NUMA node meminfo files by simply
"mimicking" a typical environment where each NUMA node returns:
- NodeMemTotal = PalMemTotal / numa_nodes_cnt
- NodeMemFree = PalMemAvailable / numa_nodes_cnt

Signed-off-by: Kailun Qin <kailun.qin@intel.com>

libos/include/libos_fs_pseudo.h

@@ -235,6 +235,7 @@ bool sys_resource_name_exists(struct libos_dentry* parent, const char* name);
 int sys_resource_list_names(struct libos_dentry* parent, readdir_callback_t callback, void* arg);
 int sys_node_general_load(struct libos_dentry* dent, char** out_data, size_t* out_size);
 int sys_node_load(struct libos_dentry* dent, char** out_data, size_t* out_size);
+int sys_node_meminfo_load(struct libos_dentry* dent, char** out_data, size_t* out_size);
 int sys_cpu_general_load(struct libos_dentry* dent, char** out_data, size_t* out_size);
 int sys_cpu_load_online(struct libos_dentry* dent, char** out_data, size_t* out_size);
 int sys_cpu_load_topology(struct libos_dentry* dent, char** out_data, size_t* out_size);

libos/src/fs/sys/fs.c

@@ -251,6 +251,7 @@ static void init_node_dir(struct pseudo_node* node) {
 
     pseudo_add_str(nodeX, "cpumap", &sys_node_load);
     pseudo_add_str(nodeX, "distance", &sys_node_load);
+    pseudo_add_str(nodeX, "meminfo", &sys_node_meminfo_load);
 
     // TODO(mkow): Does this show up for offline nodes? I never succeeded in shutting down one, even
     // after shutting down all CPUs inside the node it shows up as online on `node/online` list.

libos/src/fs/sys/node_info.c

@@ -99,3 +99,91 @@ int sys_node_load(struct libos_dentry* dent, char** out_data, size_t* out_size)
 
     return sys_load(str, out_data, out_size);
 }
+
+int sys_node_meminfo_load(struct libos_dentry* dent, char** out_data, size_t* out_size) {
+    size_t numa_nodes_cnt = g_pal_public_state->topo_info.numa_nodes_cnt;
+    /* Simply "mimic" a typical environment: split memory evenly between each NUMA node */
+    size_t node_mem_total = g_pal_public_state->mem_total / numa_nodes_cnt;
+    size_t node_mem_free = PalMemoryAvailableQuota() / numa_nodes_cnt;
+
+    assert(node_mem_total >= node_mem_free);
+
+    unsigned int node_id;
+    int ret = sys_resource_find(dent, "node", &node_id);
+    if (ret < 0)
+        return ret;
+
+    size_t size = 0, max = 256;
+    char* str = malloc(max);
+    if (!str)
+        return -ENOMEM;
+
+    /*
+     * Enumerate minimum set of node meminfo stats (the default stats in Linux, without specific
+     * `#ifdef CONFIG_xxx`). This set is based on Linux v5.19, see below for details:
+     *
+     * - https://elixir.bootlin.com/linux/v5.19/source/drivers/base/node.c#L369
+    */
+
+    struct {
+        const char* fmt;
+        unsigned long val;
+    } meminfo[] = {
+        { "Node %u MemTotal:       %8lu kB\n", node_mem_total / 1024 },
+        { "Node %u MemFree:        %8lu kB\n", node_mem_free / 1024 },
+        { "Node %u MemUsed:        %8lu kB\n", (node_mem_total - node_mem_free) / 1024 },
+        { "Node %u SwapCached:     %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Active:         %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Inactive:       %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Active(anon):   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Inactive(anon): %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Active(file):   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Inactive(file): %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Unevictable:    %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Mlocked:        %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Dirty:          %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Writeback:      %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u FilePages:      %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Mapped:         %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u AnonPages:      %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Shmem:          %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u KernelStack:    %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u PageTables:     %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u NFS_Unstable:   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Bounce:         %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u WritebackTmp:   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u KReclaimable:   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u Slab:           %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u SReclaimable:   %8lu kB\n", /*dummy value=*/0 },
+        { "Node %u SUnreclaim:     %8lu kB\n", /*dummy value=*/0 },
+    };
+
+    size_t i = 0;
+    while (i < ARRAY_SIZE(meminfo)) {
+        ret = snprintf(str + size, max - size, meminfo[i].fmt, node_id, meminfo[i].val);
+        if (ret < 0) {
+            free(str);
+            return ret;
+        }
+
+        if (size + ret >= max) {
+            max *= 2;
+            size = 0;
+            i = 0;
+            free(str);
+            /* TODO: use `realloc()` once it's available. */
+            str = malloc(max);
+            if (!str)
+                return -ENOMEM;
+
+            continue;
+        }
+
+        size += ret;
+        i++;
+    }
+
+    *out_data = str;
+    *out_size = size;
+    return 0;
+}