From 412827dc0a2e783cf036bfb03a48eb9eb0f9193b Mon Sep 17 00:00:00 2001
From: robobun <117481402+robobun@users.noreply.github.com>
Date: Tue, 14 Jul 2026 01:07:25 +0000
Subject: [PATCH] WTF: add uv_get_cgroup_current_memory()

Reads the process's cgroup's current memory usage (memory.current on cgroup
v2, memory.usage_in_bytes on cgroup v1), reusing the existing uv__slurp,
uv__read_uint64 and uv__cgroup1_find_memory_controller helpers that
uv_get_constrained_memory() already uses. Matches libuv's
uv__get_cgroup_current_memory.

Bun needs this for process.availableMemory(): Node.js documents that API as
uv_get_available_memory(), which on Linux returns (cgroup limit - cgroup
current usage) when a limit is set. The limit reader already exists here;
this adds the usage reader so bun can compute the difference without
duplicating the cgroup parsing.
---
 Source/WTF/wtf/uv_get_constrained_memory.cpp | 50 ++++++++++++++++++++
 Source/WTF/wtf/uv_get_constrained_memory.h   |  1 +
 2 files changed, 51 insertions(+)

diff --git a/Source/WTF/wtf/uv_get_constrained_memory.cpp b/Source/WTF/wtf/uv_get_constrained_memory.cpp
index 57f3748c9bc85..f69f0742fce0e 100644
--- a/Source/WTF/wtf/uv_get_constrained_memory.cpp
+++ b/Source/WTF/wtf/uv_get_constrained_memory.cpp
@@ -259,6 +259,51 @@ uint64_t uv_get_constrained_memory()
     return uv__get_cgroup_constrained_memory(buf);
 }
 
+static uint64_t uv__get_cgroup1_current_memory(char buf[1024])
+{
+    char filename[4097];
+    char* p;
+    int n;
+
+    p = uv__cgroup1_find_memory_controller(buf, &n);
+    if (p != NULL) {
+        snprintf(filename, sizeof(filename),
+            "/sys/fs/cgroup/memory/%.*s/memory.usage_in_bytes", n, p);
+        uint64_t current = uv__read_uint64(filename);
+        if (current != 0)
+            return current;
+    }
+
+    return uv__read_uint64("/sys/fs/cgroup/memory/memory.usage_in_bytes");
+}
+
+static uint64_t uv__get_cgroup2_current_memory(char buf[1024])
+{
+    char filename[4097];
+    char* p;
+    int n;
+
+    p = buf + strlen("0::/");
+    n = (int)strcspn(p, "\n");
+
+    snprintf(filename, sizeof(filename),
+        "/sys/fs/cgroup/%.*s/memory.current", n, p);
+    return uv__read_uint64(filename);
+}
+
+uint64_t uv_get_cgroup_current_memory()
+{
+    char buf[1024];
+
+    if (uv__slurp("/proc/self/cgroup", buf, sizeof(buf)))
+        return 0;
+
+    if (strncmp(buf, "0::/", 4))
+        return uv__get_cgroup1_current_memory(buf);
+
+    return uv__get_cgroup2_current_memory(buf);
+}
+
 /* Find the cgroup v1 line whose controller list contains "cpu" as a whole
  * token (it may appear as "cpu", "cpu,cpuacct", or "cpuacct,cpu"). Returns
  * a pointer to the path component (after the leading "/") and its length. */
@@ -376,6 +421,11 @@ uint64_t uv_get_constrained_memory()
     return 0;
 }
 
+uint64_t uv_get_cgroup_current_memory()
+{
+    return 0;
+}
+
 int uv_get_constrained_cpu()
 {
     return 0;
diff --git a/Source/WTF/wtf/uv_get_constrained_memory.h b/Source/WTF/wtf/uv_get_constrained_memory.h
index 2ae999118c340..06977e8f3d17a 100644
--- a/Source/WTF/wtf/uv_get_constrained_memory.h
+++ b/Source/WTF/wtf/uv_get_constrained_memory.h
@@ -1,4 +1,5 @@
 #pragma once
 
 uint64_t uv_get_constrained_memory();
+uint64_t uv_get_cgroup_current_memory();
 int uv_get_constrained_cpu();
\ No newline at end of file