From 4c3d9341fd9038a8dac0fed23dec171e17224905 Mon Sep 17 00:00:00 2001
From: Alex Cope <acope@snapchat.com>
Date: Tue, 27 Jun 2023 14:18:14 -0700
Subject: [PATCH] port changes to 6.3

---
 src/evict.cpp  | 20 +++++++++++++++++++-
 src/server.cpp | 10 ++++++++++
 src/server.h   |  1 +
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/evict.cpp b/src/evict.cpp
index 94bc132c1..aa6932e8b 100644
--- a/src/evict.cpp
+++ b/src/evict.cpp
@@ -421,10 +421,22 @@ int getMaxmemoryState(size_t *total, size_t *logical, size_t *tofree, float *lev
     if (total) *total = mem_reported;
     size_t maxmemory = g_pserver->maxmemory;
     if (fPreSnapshot)
-        maxmemory = static_cast<size_t>(maxmemory * 0.9);   // derate memory by 10% since we won't be able to free during snapshot
+        maxmemory = static_cast<size_t>(maxmemory*0.9);   // derate memory by 10% since we won't be able to free during snapshot
     if (g_pserver->FRdbSaveInProgress())
         maxmemory = static_cast<size_t>(maxmemory*1.2);
 
+    /* If there is less than 10% free system memory, force eviction */
+    bool mem_rss_max_exceeded;
+    if (g_pserver->cron_malloc_stats.sys_total) {
+        size_t mem_rss_max = static_cast<size_t>(g_pserver->cron_malloc_stats.sys_total * 0.9);
+        mem_rss_max_exceeded = g_pserver->cron_malloc_stats.process_rss > mem_rss_max;
+        if (mem_rss_max_exceeded) {
+            /* This will always set maxmemory < mem_reported */
+            float frag_ratio = (float)g_pserver->cron_malloc_stats.process_rss / (float)mem_reported;
+            maxmemory = static_cast<size_t>((float)mem_rss_max / frag_ratio);
+        }
+    }
+
     /* We may return ASAP if there is no need to compute the level. */
     int return_ok_asap = !maxmemory || mem_reported <= maxmemory;
     if (return_ok_asap && !level) return C_OK;
@@ -435,6 +447,12 @@ int getMaxmemoryState(size_t *total, size_t *logical, size_t *tofree, float *lev
     size_t overhead = freeMemoryGetNotCountedMemory();
     mem_used = (mem_used > overhead) ? mem_used-overhead : 0;
 
+     /* If we've exceeded max RSS memory, we want to force evictions no matter
+     * what so we also offset the overhead from maxmemory. */
+    if (mem_rss_max_exceeded) {
+        maxmemory = (maxmemory > overhead) ? maxmemory-overhead : 0;
+    }
+
     /* Compute the ratio of memory usage. */
     if (level) {
         if (!maxmemory) {
diff --git a/src/server.cpp b/src/server.cpp
index 663e4e8fc..d1ef097c4 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -70,6 +70,7 @@
 #ifdef __linux__
 #include <sys/prctl.h>
 #include <sys/mman.h>
+#include <sys/sysinfo.h>
 #endif
 
 int g_fTestMode = false;
@@ -2312,6 +2313,15 @@ void cronUpdateMemoryStats() {
             g_pserver->cron_malloc_stats.allocator_active = g_pserver->cron_malloc_stats.allocator_resident;
         if (!g_pserver->cron_malloc_stats.allocator_allocated)
             g_pserver->cron_malloc_stats.allocator_allocated = g_pserver->cron_malloc_stats.zmalloc_used;
+
+     #ifdef __linux__
+        struct sysinfo sysinf;
+        memset(&sysinf, 0, sizeof sysinf);
+        if (!sysinfo(&sysinf)) {
+            g_pserver->cron_malloc_stats.sys_total = static_cast<size_t>(sysinf.totalram);
+        }
+    #endif
+
     }
 }
 
diff --git a/src/server.h b/src/server.h
index 422cb9495..3a5ed977f 100644
--- a/src/server.h
+++ b/src/server.h
@@ -2014,6 +2014,7 @@ struct malloc_stats {
     size_t allocator_allocated;
     size_t allocator_active;
     size_t allocator_resident;
+    size_t sys_total;
 };
 
 typedef struct socketFds {