Free offload to IO threads

Signed-off-by: Uri Yagelnik <[email protected]>

src/db.c

@@ -32,6 +32,7 @@
 #include "latency.h"
 #include "script.h"
 #include "functions.h"
+#include "io_threads.h"
 
 #include <signal.h>
 #include <ctype.h>
@@ -297,7 +298,10 @@ static void dbSetValue(serverDb *db, robj *key, robj *val, int overwrite, dictEn
         old = dictGetVal(de);
     }
     kvstoreDictSetVal(db->keys, slot, de, val);
-    if (server.lazyfree_lazy_server_del) {
+    /* For efficiency, let the I/O thread that allocated an object also deallocate it. */
+    if (tryOffloadFreeObjToIOThreads(old) == C_OK) {
+        /* OK */
+    } else if (server.lazyfree_lazy_server_del) {
         freeObjAsync(key, old, db->id);
     } else {
         decrRefCount(old);

src/io_threads.c

@@ -124,6 +124,10 @@ int inMainThread(void) {
     return thread_id == 0;
 }
 
+int getIOThreadID(void) {
+    return thread_id;
+}
+
 /* Drains the I/O threads queue by waiting for all jobs to be processed.
  * This function must be called from the main thread. */
 void drainIOThreadsQueue(void) {
@@ -387,3 +391,101 @@ int trySendWriteToIOThreads(client *c) {
     IOJobQueue_push(jq, ioThreadWriteToClient, c);
     return C_OK;
 }
+
+/* Internal function to free the client's argv in an IO thread. */
+void IOThreadFreeArgv(void *data) {
+    robj **argv = (robj **)data;
+
+    for (int i = 0;; i++) {
+        robj *o = argv[i];
+        if (o == NULL) {
+            continue;
+        }
+
+        int allocator_id = o->allocator_id;
+        decrRefCount(o);
+
+        /* The allocator_id is set to 0 to indicate that this is the last argument to free */
+        if (allocator_id == 0) {
+            break;
+        }
+    }
+
+    zfree(argv);
+}
+
+/* This function attempts to offload the client's argv to an IO thread.
+ * Returns C_OK if the client's argv were successfully offloaded to an IO thread,
+ * C_ERR otherwise. */
+int tryOffloadFreeArgvToIOThreads(client *c) {
+    if (server.active_io_threads_num <= 1 || c->argc == 0) {
+        return C_ERR;
+    }
+
+    size_t tid = (c->id % (server.active_io_threads_num - 1)) + 1;
+
+    IOJobQueue *jq = &io_jobs[tid];
+    if (IOJobQueue_isFull(jq)) {
+        return C_ERR;
+    }
+
+    int last_arg_to_free = -1;
+
+    /* Prepare the argv */
+    for (int j = 0; j < c->argc; j++) {
+        if (c->argv[j]->refcount > 1 || tid != c->argv[j]->allocator_id) {
+            decrRefCount(c->argv[j]);
+            /* Set argv[j] to NULL to avoid double free */
+            c->argv[j] = NULL;
+        } else {
+            last_arg_to_free = j;
+        }
+    }
+
+    /* If no argv to free, free the argv array at the main thread */
+    if (last_arg_to_free == -1) {
+        zfree(c->argv);
+        return C_OK;
+    }
+
+    /* We set the allocator_id of the last arg to free to 0 to indicate that
+     * this is the last argument to free. With this approach, we don't need to
+     * send the argc to the IO thread and we can send just the argv ptr. */
+    c->argv[last_arg_to_free]->allocator_id = 0;
+
+    /* Must succeed as we checked the free space before. */
+    IOJobQueue_push(jq, IOThreadFreeArgv, c->argv);
+
+    return C_OK;
+}
+
+/* This function attempts to offload the free of an object to an IO thread.
+ * Returns C_OK if the object was successfully offloaded to an IO thread,
+ * C_ERR otherwise.*/
+int tryOffloadFreeObjToIOThreads(robj *obj) {
+    if (server.active_io_threads_num <= 1) {
+        return C_ERR;
+    }
+    /* the object was not allocated by the IO threads */
+    if (obj->allocator_id == 0) return C_ERR;
+
+    if (obj->refcount > 1) return C_ERR;
+
+    int tid = obj->allocator_id;
+    /* If the thread that allocated the object is no longer active,
+     * reassign the object to a different thread. This is necessary
+     * because we dynamically adjust the number of active threads
+     * based on I/O load.*/
+    if (tid >= server.active_io_threads_num) {
+        tid = (tid % (server.active_io_threads_num - 1)) + 1;
+    }
+
+    IOJobQueue *jq = &io_jobs[tid];
+    if (IOJobQueue_isFull(jq)) {
+        return C_ERR;
+    }
+
+    IOJobQueue_push(jq, decrRefCountVoid, obj);
+    server.stat_io_freed_objects++;
+    return C_OK;
+}

src/io_threads.h

@@ -6,8 +6,11 @@
 void initIOThreads(void);
 void killIOThreads(void);
 int inMainThread(void);
+int getIOThreadID(void);
 int trySendReadToIOThreads(client *c);
 int trySendWriteToIOThreads(client *c);
+int tryOffloadFreeObjToIOThreads(robj *o);
+int tryOffloadFreeArgvToIOThreads(client *c);
 void adjustIOThreadsByEventLoad(int numevents, int increase_only);
 void drainIOThreadsQueue(void);
 

src/networking.c

@@ -1424,14 +1424,15 @@ void freeClientOriginalArgv(client *c) {
 }
 
 void freeClientArgv(client *c) {
-    int j;
-    for (j = 0; j < c->argc; j++) decrRefCount(c->argv[j]);
+    if (tryOffloadFreeArgvToIOThreads(c) == C_ERR) {
+        for (int j = 0; j < c->argc; j++) decrRefCount(c->argv[j]);
+        zfree(c->argv);
+    }
     c->argc = 0;
     c->cmd = NULL;
     c->io_parsed_cmd = NULL;
     c->argv_len_sum = 0;
     c->argv_len = 0;
-    zfree(c->argv);
     c->argv = NULL;
 }
 
@@ -4646,6 +4647,9 @@ void ioThreadReadQueryFromClient(void *data) {
         goto done;
     }
 
+    /* set the allocator ID for the objects */
+    for (int i = 0; i < c->argc; i++) c->argv[i]->allocator_id = getIOThreadID();
+
     /* Lookup command offload */
     c->io_parsed_cmd = lookupCommand(c->argv, c->argc);
     if (c->io_parsed_cmd && commandCheckArity(c->io_parsed_cmd, c->argc, NULL) == 0) {

src/object.c

@@ -46,6 +46,7 @@ robj *createObject(int type, void *ptr) {
     o->encoding = OBJ_ENCODING_RAW;
     o->ptr = ptr;
     o->refcount = 1;
+    o->allocator_id = 0;
     o->lru = 0;
     return o;
 }
@@ -96,6 +97,7 @@ robj *createEmbeddedStringObject(const char *ptr, size_t len) {
     o->encoding = OBJ_ENCODING_EMBSTR;
     o->ptr = sh + 1;
     o->refcount = 1;
+    o->allocator_id = 0;
     o->lru = 0;
 
     sh->len = len;

src/server.c

@@ -2492,6 +2492,7 @@ void resetServerStats(void) {
     server.stat_io_reads_processed = 0;
     server.stat_total_reads_processed = 0;
     server.stat_io_writes_processed = 0;
+    server.stat_io_freed_objects = 0;
     server.stat_total_writes_processed = 0;
     server.stat_client_qbuf_limit_disconnections = 0;
     server.stat_client_outbuf_limit_disconnections = 0;
@@ -5702,6 +5703,7 @@ sds genValkeyInfoString(dict *section_dict, int all_sections, int everything) {
             "total_writes_processed:%lld\r\n", server.stat_total_writes_processed,
             "io_threaded_reads_processed:%lld\r\n", server.stat_io_reads_processed,
             "io_threaded_writes_processed:%lld\r\n", server.stat_io_writes_processed,
+            "io_threaded_freed_objects:%lld\r\n", server.stat_io_freed_objects,
             "client_query_buffer_limit_disconnections:%lld\r\n", server.stat_client_qbuf_limit_disconnections,
             "client_output_buffer_limit_disconnections:%lld\r\n", server.stat_client_outbuf_limit_disconnections,
             "reply_buffer_shrinks:%lld\r\n", server.stat_reply_buffer_shrinks,

src/server.h

@@ -853,16 +853,18 @@ struct ValkeyModuleDigest {
 #define LRU_CLOCK_MAX ((1 << LRU_BITS) - 1) /* Max value of obj->lru */
 #define LRU_CLOCK_RESOLUTION 1000           /* LRU clock resolution in ms */
 
-#define OBJ_SHARED_REFCOUNT INT_MAX       /* Global object never destroyed. */
-#define OBJ_STATIC_REFCOUNT (INT_MAX - 1) /* Object allocated in the stack. */
+#define UINT28_MAX 0x0FFFFFFF
+#define OBJ_SHARED_REFCOUNT UINT28_MAX       /* Global object never destroyed. */
+#define OBJ_STATIC_REFCOUNT (UINT28_MAX - 1) /* Object allocated in the stack. */
 #define OBJ_FIRST_SPECIAL_REFCOUNT OBJ_STATIC_REFCOUNT
 struct serverObject {
     unsigned type : 4;
     unsigned encoding : 4;
     unsigned lru : LRU_BITS; /* LRU time (relative to global lru_clock) or
                               * LFU data (least significant 8 bits frequency
                               * and most significant 16 bits access time). */
-    int refcount;
+    unsigned refcount : 28;
+    unsigned allocator_id : 4;
     void *ptr;
 };
 
@@ -1751,6 +1753,7 @@ struct valkeyServer {
     long long stat_dump_payload_sanitizations;         /* Number deep dump payloads integrity validations. */
     long long stat_io_reads_processed;                 /* Number of read events processed by IO threads */
     long long stat_io_writes_processed;                /* Number of write events processed by IO threads */
+    long long stat_io_freed_objects;                   /* Number of objects freed by IO threads */
     long long stat_total_reads_processed;              /* Total number of read events processed */
     long long stat_total_writes_processed;             /* Total number of write events processed */
     long long stat_client_qbuf_limit_disconnections;   /* Total number of clients reached query buf length limit */