From 7694dbc82175baff3b3a42898ef8c29c7299eca3 Mon Sep 17 00:00:00 2001
From: Benny Baumann <BenBE@geshi.org>
Date: Sun, 29 May 2022 21:17:25 +0200
Subject: [PATCH] Implement PCP support for minimum ZFS ARC size

---
 pcp/PCPMetric.h      |  1 +
 pcp/PCPProcessList.c |  2 ++
 pcp/Platform.c       | 10 ++++++++--
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/pcp/PCPMetric.h b/pcp/PCPMetric.h
index aa0e2a7a..84ccbb95 100644
--- a/pcp/PCPMetric.h
+++ b/pcp/PCPMetric.h
@@ -81,6 +81,7 @@ typedef enum PCPMetric_ {
    PCP_ZFS_ARC_BONUS_SIZE,      /* zfs.arc.bonus_size */
    PCP_ZFS_ARC_COMPRESSED_SIZE, /* zfs.arc.compressed_size */
    PCP_ZFS_ARC_UNCOMPRESSED_SIZE, /* zfs.arc.uncompressed_size */
+   PCP_ZFS_ARC_C_MIN,           /* zfs.arc.c_min */
    PCP_ZFS_ARC_C_MAX,           /* zfs.arc.c_max */
    PCP_ZFS_ARC_DBUF_SIZE,       /* zfs.arc.dbuf_size */
    PCP_ZFS_ARC_DNODE_SIZE,      /* zfs.arc.dnode_size */
diff --git a/pcp/PCPProcessList.c b/pcp/PCPProcessList.c
index ca82575a..045f7ae0 100644
--- a/pcp/PCPProcessList.c
+++ b/pcp/PCPProcessList.c
@@ -601,6 +601,8 @@ static inline void PCPProcessList_scanZfsArcstats(PCPProcessList* this) {
    memset(&this->zfs, 0, sizeof(ZfsArcStats));
    if (PCPMetric_values(PCP_ZFS_ARC_ANON_SIZE, &value, 1, PM_TYPE_U64))
       this->zfs.anon = value.ull / ONE_K;
+   if (PCPMetric_values(PCP_ZFS_ARC_C_MIN, &value, 1, PM_TYPE_U64))
+      this->zfs.min = value.ull / ONE_K;
    if (PCPMetric_values(PCP_ZFS_ARC_C_MAX, &value, 1, PM_TYPE_U64))
       this->zfs.max = value.ull / ONE_K;
    if (PCPMetric_values(PCP_ZFS_ARC_BONUS_SIZE, &value, 1, PM_TYPE_U64))
diff --git a/pcp/Platform.c b/pcp/Platform.c
index b3d6ed4a..342bf439 100644
--- a/pcp/Platform.c
+++ b/pcp/Platform.c
@@ -178,6 +178,7 @@ static const char* Platform_metricNames[] = {
    [PCP_ZFS_ARC_BONUS_SIZE] = "zfs.arc.bonus_size",
    [PCP_ZFS_ARC_COMPRESSED_SIZE] = "zfs.arc.compressed_size",
    [PCP_ZFS_ARC_UNCOMPRESSED_SIZE] = "zfs.arc.uncompressed_size",
+   [PCP_ZFS_ARC_C_MIN] = "zfs.arc.c_min",
    [PCP_ZFS_ARC_C_MAX] = "zfs.arc.c_max",
    [PCP_ZFS_ARC_DBUF_SIZE] = "zfs.arc.dbuf_size",
    [PCP_ZFS_ARC_DNODE_SIZE] = "zfs.arc.dnode_size",
@@ -510,8 +511,13 @@ void Platform_setMemoryValues(Meter* this) {
    this->values[4] = pl->availableMem;
 
    if (ppl->zfs.enabled != 0) {
-      this->values[0] -= ppl->zfs.size;
-      this->values[3] += ppl->zfs.size;
+      // ZFS does not shrink below the value of zfs_arc_min.
+      unsigned long long int shrinkableSize = 0;
+      if (ppl->zfs.size > ppl->zfs.min)
+         shrinkableSize = ppl->zfs.size - ppl->zfs.min;
+      this->values[0] -= shrinkableSize;
+      this->values[3] += shrinkableSize;
+      this->values[4] += shrinkableSize;
    }
 }