From c575d3e82f18a802948db93f14ec6886ded1007d Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@collectd.org>
Date: Thu, 4 Jan 2024 08:58:14 +0100
Subject: [PATCH] memory plugin: Remove "slab" and "available" memory.

Under Linux, the plugin reported "slab" (kernel data structures cache) and
"available" (estimate of how much memory might be available without swapping).
These metrics group memory along different dimensions than other reported
memory, leading to double counting of some memory. The result was that the sum
of all memory metrics was not constant.
---
 src/memory.c | 49 +++----------------------------------------------
 1 file changed, 3 insertions(+), 46 deletions(-)

diff --git a/src/memory.c b/src/memory.c
index 51d63179c..a75191761 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -69,9 +69,6 @@ typedef enum {
   STATE_FREE,
   STATE_BUFFERS,
   STATE_CACHED,
-  STATE_SLAB_TOTAL,
-  STATE_SLAB_RECL,
-  STATE_SLAB_UNRECL,
   STATE_WIRED,
   STATE_ACTIVE,
   STATE_INACTIVE,
@@ -79,30 +76,15 @@ typedef enum {
   STATE_LOCKED,
   STATE_ARC,
   STATE_UNUSED,
-  STATE_AVAILABLE,
   STATE_USER_WIRE,
   STATE_LAUNDRY,
   STATE_MAX, /* #states */
 } memory_type_t;
 
 static char const *memory_type_names[STATE_MAX] = {
-    "used",
-    "free",
-    "buffers",
-    "cached",
-    "slab",
-    "slab_reclaimable",
-    "slab_unreclaimable",
-    "wired",
-    "active",
-    "inactive",
-    "kernel",
-    "locked",
-    "arc",
-    "unusable",
-    "available",
-    "user_wire",
-    "laundry",
+    "used",     "free",      "buffers", "cached", "wired",
+    "active",   "inactive",  "kernel",  "locked", "arc",
+    "unusable", "user_wire", "laundry",
 };
 
 /* vm_statistics_data_t */
@@ -463,14 +445,6 @@ static int memory_read_internal(gauge_t values[STATE_MAX]) {
     } else if (strcmp(fields[0], "Cached:") == 0) {
       values[STATE_CACHED] = v;
       mem_not_used += v;
-    } else if (strcmp(fields[0], "Slab:") == 0) {
-      values[STATE_SLAB_TOTAL] = v;
-    } else if (strcmp(fields[0], "SReclaimable:") == 0) {
-      values[STATE_SLAB_RECL] = v;
-    } else if (strcmp(fields[0], "SUnreclaim:") == 0) {
-      values[STATE_SLAB_UNRECL] = v;
-    } else if (strcmp(fields[0], "MemAvailable:") == 0) {
-      values[STATE_AVAILABLE] = v;
     }
   }
 
@@ -478,15 +452,6 @@ static int memory_read_internal(gauge_t values[STATE_MAX]) {
     WARNING("memory plugin: fclose failed: %s", STRERRNO);
   }
 
-  /* If SReclaimable (introduced in kernel 2.6.19) is available count it
-   * (but not SUnreclaim) towards the unused memory.
-   * If we do not have detailed slab info count the total as unused. */
-  if (!isnan(values[STATE_SLAB_RECL])) {
-    mem_not_used += values[STATE_SLAB_RECL];
-  } else if (!isnan(values[STATE_SLAB_TOTAL])) {
-    mem_not_used += values[STATE_SLAB_TOTAL];
-  }
-
   if (isnan(mem_total) || (mem_total == 0) || (mem_total < mem_not_used)) {
     return EINVAL;
   }
@@ -494,14 +459,6 @@ static int memory_read_internal(gauge_t values[STATE_MAX]) {
   /* "used" is not explicitly reported. It is calculated as everything that is
    * not "not used", e.g. cached, buffers, ... */
   values[STATE_USED] = mem_total - mem_not_used;
-
-  /* SReclaimable and SUnreclaim were introduced in kernel 2.6.19
-   * They sum up to the value of Slab, which is available on older & newer
-   * kernels. So SReclaimable/SUnreclaim are submitted if available, and Slab
-   * if not. */
-  if (!isnan(values[STATE_SLAB_RECL]) || !isnan(values[STATE_SLAB_UNRECL])) {
-    values[STATE_SLAB_TOTAL] = NAN;
-  }
   /* #endif KERNEL_LINUX */
 
 #elif HAVE_LIBKSTAT
-- 
2.39.5