From 0c908cddf897670bd364874c55ad86063a3f82c8 Mon Sep 17 00:00:00 2001
From: Dov Murik <dov.murik1@il.ibm.com>
Date: Mon, 27 Jun 2022 08:21:59 +0000
Subject: [PATCH] memory: set_kmem_limit: ignore Unsupported error

Setting (writing into) `memory.kmem.limit_in_bytes` is not supported in
Linux kernel >= 5.16 (see kernel commit 58056f77502: "memcg, kmem:
further deprecate kmem.limit_in_bytes"):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=58056f77502

If the write call in `set_kmem_limit()` returns EOPNOTSUPP, log a
warning message but ignore the error (do nothing).

Add a unit-test for `set_kmem_limit` in cgroups v1.

Fix #81

Signed-off-by: Dov Murik <dov.murik1@il.ibm.com>
---
 src/memory.rs    | 12 ++++++++++--
 tests/builder.rs |  3 ++-
 tests/memory.rs  | 15 +++++++++++++++
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/memory.rs b/src/memory.rs
index 7b02e1f..216af30 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -8,6 +8,7 @@
 //!
 //! See the Kernel's documentation for more information about this subsystem, found at:
 //!  [Documentation/cgroup-v1/memory.txt](https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt)
+use log::warn;
 use std::collections::HashMap;
 use std::io::Write;
 use std::path::PathBuf;
@@ -840,8 +841,15 @@ impl MemController {
 
         self.open_path("memory.kmem.limit_in_bytes", true)
             .and_then(|mut file| {
-                file.write_all(limit.to_string().as_ref())
-                    .map_err(|e| Error::with_cause(WriteFailed, e))
+                let r = file.write_all(limit.to_string().as_ref());
+                match r {
+                    Ok(()) => Ok(()),
+                    Err(ref e) if e.raw_os_error() == Some(libc::EOPNOTSUPP) => {
+                        warn!("memory.kmem.limit_in_bytes is unsupported by the kernel");
+                        Ok(())
+                    }
+                    Err(e) => Err(Error::with_cause(WriteFailed, e)),
+                }
             })
     }
 
diff --git a/tests/builder.rs b/tests/builder.rs
index 0650806..e91d3c9 100644
--- a/tests/builder.rs
+++ b/tests/builder.rs
@@ -47,7 +47,8 @@ pub fn test_memory_res_build() {
     {
         let c: &MemController = cg.controller_of().unwrap();
         if !c.v2() {
-            assert_eq!(c.kmem_stat().limit_in_bytes, 128 * 1024 * 1024);
+            // Note: we don't tests the value of c.kmem_stat().limit_in_bytes because on Linux
+            // kernel >= 5.16 setting this value is unsupported.
             assert_eq!(c.memory_stat().swappiness, 70);
         }
         assert_eq!(c.memory_stat().limit_in_bytes, 1024 * 1024 * 1024);
diff --git a/tests/memory.rs b/tests/memory.rs
index 6667ed4..2decc97 100644
--- a/tests/memory.rs
+++ b/tests/memory.rs
@@ -33,6 +33,21 @@ fn test_disable_oom_killer() {
     cg.delete().unwrap();
 }
 
+#[test]
+fn set_kmem_limit_v1() {
+    let h = cgroups_rs::hierarchies::auto();
+    if h.v2() {
+        return;
+    }
+
+    let cg = Cgroup::new(h, String::from("set_kmem_limit_v1"));
+    {
+        let mem_controller: &MemController = cg.controller_of().unwrap();
+        mem_controller.set_kmem_limit(1).unwrap();
+    }
+    cg.delete().unwrap();
+}
+
 #[test]
 fn set_mem_v2() {
     let h = cgroups_rs::hierarchies::auto();