feat(dbengine): make dbengine page cache undumpable and dedupuble (#12765)

* make netdata more awesome

* reworked on-madvise and mmap to provide clarity

6 files changed, 29 insertions, 18 deletions

diff --git a/database/engine/pagecache.c b/database/engine/pagecache.c
index 40e24b321c..43734b0dd5 100644
--- a/database/engine/pagecache.c
+++ b/database/engine/pagecache.c
@@ -356,7 +356,7 @@ static void pg_cache_evict_unsafe(struct rrdengine_instance *ctx, struct rrdeng_
 {
     struct page_cache_descr *pg_cache_descr = descr->pg_cache_descr;
 
-    freez(pg_cache_descr->page);
+    dbengine_page_free(pg_cache_descr->page);
     pg_cache_descr->page = NULL;
     pg_cache_descr->flags &= ~RRD_PAGE_POPULATED;
     pg_cache_release_pages_unsafe(ctx, 1);
@@ -1222,7 +1222,7 @@ void free_page_cache(struct rrdengine_instance *ctx)
                 /* Check rrdenglocking.c */
                 pg_cache_descr = descr->pg_cache_descr;
                 if (pg_cache_descr->flags & RRD_PAGE_POPULATED) {
-                    freez(pg_cache_descr->page);
+                    dbengine_page_free(pg_cache_descr->page);
                     bytes_freed += RRDENG_BLOCK_SIZE;
                 }
                 rrdeng_destroy_pg_cache_descr(ctx, pg_cache_descr);
diff --git a/database/engine/rrdengine.c b/database/engine/rrdengine.c
index f47738aea2..5631a1df3c 100644
--- a/database/engine/rrdengine.c
+++ b/database/engine/rrdengine.c
@@ -11,6 +11,16 @@ rrdeng_stats_t global_flushing_pressure_page_deletions = 0;
 
 static unsigned pages_per_extent = MAX_PAGES_PER_EXTENT;
 
+void *dbengine_page_alloc() {
+    void *page = netdata_mmap(NULL, RRDENG_BLOCK_SIZE, MAP_PRIVATE, enable_ksm);
+    if(!page) fatal("Cannot allocate dbengine page cache page, with mmap()");
+    return page;
+}
+
+void dbengine_page_free(void *page) {
+    munmap(page, RRDENG_BLOCK_SIZE);
+}
+
 static void sanity_check(void)
 {
     /* Magic numbers must fit in the super-blocks */
@@ -176,7 +186,7 @@ void read_cached_extent_cb(struct rrdengine_worker_config* wc, unsigned idx, str
     struct extent_info *extent = xt_io_descr->descr_array[0]->extent;
 
     for (i = 0 ; i < xt_io_descr->descr_count; ++i) {
-        page = mallocz(RRDENG_BLOCK_SIZE);
+        page = dbengine_page_alloc();
         descr = xt_io_descr->descr_array[i];
         for (j = 0, page_offset = 0 ; j < extent->number_of_pages ; ++j) {
             /* care, we don't hold the descriptor mutex */
@@ -331,7 +341,7 @@ after_crc_check:
                 continue; /* Failed to reserve a suitable page */
             is_prefetched_page = 1;
         }
-        page = mallocz(RRDENG_BLOCK_SIZE);
+        page = dbengine_page_alloc();
 
         /* care, we don't hold the descriptor mutex */
         if (have_read_error) {
diff --git a/database/engine/rrdengine.h b/database/engine/rrdengine.h
index b0c8e4d02d..7aba98e451 100644
--- a/database/engine/rrdengine.h
+++ b/database/engine/rrdengine.h
@@ -227,6 +227,9 @@ struct rrdengine_instance {
     struct rrdengine_statistics stats;
 };
 
+extern void *dbengine_page_alloc(void);
+extern void dbengine_page_free(void *page);
+
 extern int init_rrd_files(struct rrdengine_instance *ctx);
 extern void finalize_rrd_files(struct rrdengine_instance *ctx);
 extern void rrdeng_test_quota(struct rrdengine_worker_config* wc);
diff --git a/database/engine/rrdengineapi.c b/database/engine/rrdengineapi.c
index 6ebee1459f..e94f6e003d 100755
--- a/database/engine/rrdengineapi.c
+++ b/database/engine/rrdengineapi.c
@@ -202,7 +202,7 @@ void rrdeng_store_metric_flush_current_page(RRDDIM *rd)
             /* handle->prev_descr = descr;*/
         }
     } else {
-        freez(descr->pg_cache_descr->page);
+        dbengine_page_free(descr->pg_cache_descr->page);
         rrdeng_destroy_pg_cache_descr(ctx, descr->pg_cache_descr);
         freez(descr);
     }
@@ -724,7 +724,7 @@ void *rrdeng_create_page(struct rrdengine_instance *ctx, uuid_t *id, struct rrde
 
     descr = pg_cache_create_descr();
     descr->id = id; /* TODO: add page type: metric, log, something? */
-    page = mallocz(RRDENG_BLOCK_SIZE); /*TODO: add page size */
+    page = dbengine_page_alloc(); /*TODO: add page size */
     rrdeng_page_descr_mutex_lock(ctx, descr);
     pg_cache_descr = descr->pg_cache_descr;
     pg_cache_descr->page = page;
diff --git a/database/rrddim.c b/database/rrddim.c
index df45363bc7..3c013e1ded 100644
--- a/database/rrddim.c
+++ b/database/rrddim.c
@@ -244,12 +244,11 @@ RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collecte
 
     if(memory_mode == RRD_MEMORY_MODE_SAVE || memory_mode == RRD_MEMORY_MODE_MAP ||
        memory_mode == RRD_MEMORY_MODE_RAM) {
-        rd = (RRDDIM *)mymmap(
-                  (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename
-                , size
-                , ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE)
-                , 1
-        );
+        rd = (RRDDIM *)netdata_mmap(
+            (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename,
+            size,
+            ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE),
+            1);
 
         if(likely(rd)) {
             // we have a file mapped for rd
diff --git a/database/rrdset.c b/database/rrdset.c
index 1793d87546..d0764cc281 100644
--- a/database/rrdset.c
+++ b/database/rrdset.c
@@ -744,12 +744,11 @@ RRDSET *rrdset_create_custom(
     snprintfz(fullfilename, FILENAME_MAX, "%s/main.db", cache_dir);
     if(memory_mode == RRD_MEMORY_MODE_SAVE || memory_mode == RRD_MEMORY_MODE_MAP ||
        memory_mode == RRD_MEMORY_MODE_RAM) {
-        st = (RRDSET *) mymmap(
-                  (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename
-                , size
-                , ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE)
-                , 0
-        );
+        st = (RRDSET *)netdata_mmap(
+            (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename,
+            size,
+            ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE),
+            0);
 
         if(st) {
             memset(&st->avl, 0, sizeof(avl_t));