do not use mmap when the mmap limit is too low (netdata#19714)

CMakeLists.txt

@@ -1056,6 +1056,8 @@ set(LIBNETDATA_FILES
         src/libnetdata/os/run_dir.h
         src/libnetdata/os/file_lock.c
         src/libnetdata/os/file_lock.h
+        src/libnetdata/os/mmap_limit.c
+        src/libnetdata/os/mmap_limit.h
 )
 
 list(APPEND LIBNETDATA_FILES ${INICFG_FILES})

src/libnetdata/aral/aral.c

@@ -143,6 +143,15 @@ struct aral {
 #define aral_pages_head_free(ar, marked) (marked ? &ar->aral_lock.pages_marked_free : &ar->aral_lock.pages_free)
 #define aral_pages_head_full(ar, marked) (marked ? &ar->aral_lock.pages_marked_full : &ar->aral_lock.pages_full)
 
+static inline bool aral_malloc_use_mmap(ARAL *ar __maybe_unused, size_t size) {
+    unsigned long long mmap_limit = os_mmap_limit();
+
+    if(mmap_limit > 256 * 1000 && size >= ARAL_MALLOC_USE_MMAP_ABOVE)
+        return true;
+
+    return false;
+}
+
 const char *aral_name(ARAL *ar) {
     return ar->config.name;
 }
@@ -503,7 +512,7 @@ static ALWAYS_INLINE size_t aral_next_allocation_size___adders_lock_needed(ARAL
         ar->ops[idx].adders.allocation_size = size;
     }
 
-    if(!ar->config.mmap.enabled && size < ARAL_MALLOC_USE_MMAP_ABOVE) {
+    if(!ar->config.mmap.enabled && aral_malloc_use_mmap(ar, size)) {
         // when doing malloc, don't allocate entire pages, but only what needed
         size =
             aral_elements_in_page_size(ar, size) * ar->config.element_size +
@@ -553,7 +562,7 @@ static ARAL_PAGE *aral_create_page___no_lock_needed(ARAL *ar, size_t size TRACE_
     else {
         size_t ARAL_PAGE_size = memory_alignment(sizeof(ARAL_PAGE), SYSTEM_REQUIRED_ALIGNMENT);
 
-        if (size >= ARAL_MALLOC_USE_MMAP_ABOVE) {
+        if (aral_malloc_use_mmap(ar, size)) {
             bool mapped;
             uint8_t *ptr =
                 nd_mmap_advanced(NULL, size, MAP_ANONYMOUS | MAP_PRIVATE, 1, false, ar->config.options & ARAL_DONT_DUMP, NULL);

src/libnetdata/os/mmap_limit.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "mmap_limit.h"
+#include "libnetdata/libnetdata.h"
+
+unsigned long long os_mmap_limit(void) {
+    static unsigned long long cached_limit = 0;
+
+    if (cached_limit)
+        return cached_limit;
+
+#if defined(OS_LINUX)
+    if(read_single_number_file("/proc/sys/vm/max_map_count", &cached_limit) != 0)
+        cached_limit = 65536;
+#else
+    // For other operating systems, assume no limit.
+    cached_limit = UINT32_MAX;
+#endif
+
+    return cached_limit;
+}

src/libnetdata/os/mmap_limit.h

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_MMAP_LIMIT_H
+#define NETDATA_MMAP_LIMIT_H
+
+#include "libnetdata/common.h"
+
+unsigned long long os_mmap_limit(void);
+
+#endif //NETDATA_MMAP_LIMIT_H

src/libnetdata/os/os.h

@@ -39,6 +39,7 @@
 #include "boot_id.h"
 #include "run_dir.h"
 #include "file_lock.h"
+#include "mmap_limit.h"
 
 // this includes windows.h to the whole of netdata
 // so various conflicts arise