refactor(arena): use a shared block freelist

This is both simpler in client code and more effective (always reuse
block hottest in cache)

15 files changed, 49 insertions, 61 deletions

diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 5db584f6a8..cacac91ee8 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -114,8 +114,6 @@ static char *e_listblobarg = N_("E899: Argument of %s must be a List or Blob");
 static char *e_invalwindow = N_("E957: Invalid window number");
 static char *e_reduceempty = N_("E998: Reduce of an empty %s with no initial value");
 
-static ArenaMem eval_reuse_blk = NULL;
-
 /// Dummy va_list for passing to vim_snprintf
 ///
 /// Used because:
@@ -281,10 +279,6 @@ static void api_wrapper(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 
   Error err = ERROR_INIT;
   Arena res_arena = ARENA_EMPTY;
-  if (handler.arena_return) {
-    // TODO(bfredl): also use arena for vim_to_object
-    arena_start(&res_arena, &eval_reuse_blk);
-  }
   Object result = handler.fn(VIML_INTERNAL_CALL, args, &res_arena, &err);
 
   if (ERROR_SET(&err)) {
@@ -299,7 +293,7 @@ static void api_wrapper(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 end:
   api_free_array(args);
   if (handler.arena_return) {
-    arena_mem_free(arena_finish(&res_arena), &eval_reuse_blk);
+    arena_mem_free(arena_finish(&res_arena));
   } else {
     api_free_object(result);
   }
@@ -6885,7 +6879,6 @@ static void f_rpcrequest(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   uint64_t chan_id = (uint64_t)argvars[0].vval.v_number;
   const char *method = tv_get_string(&argvars[1]);
 
-  // TODO: putta in eval_reuse_blk
   ArenaMem res_mem = NULL;
   Object result = rpc_send_call(chan_id, method, args, &res_mem, &err);
 
@@ -6921,7 +6914,7 @@ static void f_rpcrequest(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   }
 
 end:
-  arena_mem_free(res_mem, &eval_reuse_blk);
+  arena_mem_free(res_mem);
   api_clear_error(&err);
 }
 
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 9a7b093282..ef6e1cbb22 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -3154,7 +3154,6 @@ draw_cmdline_no_arabicshape:
 static void ui_ext_cmdline_show(CmdlineInfo *line)
 {
   Arena arena = ARENA_EMPTY;
-  arena_start(&arena, &ui_ext_fixblk);
   Array content;
   if (cmdline_star) {
     content = arena_array(&arena, 1);
@@ -3199,7 +3198,7 @@ static void ui_ext_cmdline_show(CmdlineInfo *line)
                                  line->special_shift,
                                  line->level);
   }
-  arena_mem_free(arena_finish(&arena), &ui_ext_fixblk);
+  arena_mem_free(arena_finish(&arena));
 }
 
 void ui_ext_cmdline_block_append(size_t indent, const char *line)
diff --git a/src/nvim/generators/gen_api_dispatch.lua b/src/nvim/generators/gen_api_dispatch.lua
index e4798bf5ce..67b8f5f0f5 100644
--- a/src/nvim/generators/gen_api_dispatch.lua
+++ b/src/nvim/generators/gen_api_dispatch.lua
@@ -413,8 +413,6 @@ output:write([[
 #include "nvim/lua/executor.h"
 #include "nvim/memory.h"
 
-static ArenaMem lua_reuse_blk = { 0 };
-
 ]])
 include_headers(output, headers)
 output:write('\n')
@@ -496,7 +494,6 @@ local function process_function(fn)
     cparams = cparams .. '&arena, '
     write_shifted_output(output, [[
     Arena arena = ARENA_EMPTY;
-    arena_start(&arena, &lua_reuse_blk);
     ]])
   end
 
@@ -536,7 +533,7 @@ local function process_function(fn)
     end
     local free_retval
     if fn.arena_return then
-      free_retval = "arena_mem_free(arena_finish(&arena), &lua_reuse_blk);"
+      free_retval = "arena_mem_free(arena_finish(&arena));"
     else
       free_retval = "api_free_"..return_type:lower().."(ret);"
     end
diff --git a/src/nvim/highlight_group.c b/src/nvim/highlight_group.c
index 65a50df274..3bdaee8066 100644
--- a/src/nvim/highlight_group.c
+++ b/src/nvim/highlight_group.c
@@ -1303,7 +1303,7 @@ void free_highlight(void)
 {
   ga_clear(&highlight_ga);
   map_destroy(cstr_t, int)(&highlight_unames);
-  arena_mem_free(arena_finish(&highlight_arena), NULL);
+  arena_mem_free(arena_finish(&highlight_arena));
 }
 
 #endif
diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index d1d1480696..8316ab3bd1 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -1093,7 +1093,7 @@ static int nlua_rpc(lua_State *lstate, bool request)
     Object result = rpc_send_call(chan_id, name, args, &res_mem, &err);
     if (!ERROR_SET(&err)) {
       nlua_push_Object(lstate, result, false);
-      arena_mem_free(res_mem, NULL);
+      arena_mem_free(res_mem);
     }
   } else {
     if (!rpc_send_event(chan_id, name, args)) {
diff --git a/src/nvim/memory.c b/src/nvim/memory.c
index 91f066f458..7b4b104ec7 100644
--- a/src/nvim/memory.c
+++ b/src/nvim/memory.c
@@ -60,6 +60,8 @@ void try_to_free_memory(void)
   // Try to save all buffers and release as many blocks as possible
   mf_release_all();
 
+  arena_free_reuse_blks();
+
   trying_to_free = false;
 }
 
@@ -528,23 +530,18 @@ void time_to_bytes(time_t time_, uint8_t buf[8])
 }
 
 #define ARENA_BLOCK_SIZE 4096
+#define REUSE_MAX 4
 
-void arena_start(Arena *arena, ArenaMem *reuse_blk)
-{
-  if (reuse_blk && *reuse_blk) {
-    arena->cur_blk = (char *)(*reuse_blk);
-    *reuse_blk = NULL;
-    arena->size = ARENA_BLOCK_SIZE;
-    arena->pos = 0;
+static struct consumed_blk *arena_reuse_blk;
+static size_t arena_reuse_blk_count = 0;
 
-    // address is the same as as (struct consumed_blk *)arena->cur_blk
-    struct consumed_blk *blk = arena_alloc(arena, sizeof(struct consumed_blk), true);
-    assert((char *)blk == (char *)arena->cur_blk);
-    blk->prev = NULL;
-  } else {
-    arena->cur_blk = NULL;
-    arena->size = 0;
-    arena->pos = 0;
+static void arena_free_reuse_blks(void)
+{
+  while (arena_reuse_blk_count > 0) {
+    struct consumed_blk *blk = arena_reuse_blk;
+    arena_reuse_blk = arena_reuse_blk->prev;
+    xfree(blk);
+    arena_reuse_blk_count--;
   }
 }
 
@@ -564,12 +561,18 @@ ArenaMem arena_finish(Arena *arena)
 void alloc_block(Arena *arena)
 {
   struct consumed_blk *prev_blk = (struct consumed_blk *)arena->cur_blk;
-  arena->cur_blk = xmalloc(ARENA_BLOCK_SIZE);
+  if (arena_reuse_blk_count > 0) {
+    arena->cur_blk = (char *)arena_reuse_blk;
+    arena_reuse_blk = arena_reuse_blk->prev;
+    arena_reuse_blk_count--;
+  } else {
+    arena_alloc_count++;
+    arena->cur_blk = xmalloc(ARENA_BLOCK_SIZE);
+  }
   arena->pos = 0;
   arena->size = ARENA_BLOCK_SIZE;
   struct consumed_blk *blk = arena_alloc(arena, sizeof(struct consumed_blk), true);
   blk->prev = prev_blk;
-  arena_alloc_count++;
 }
 
 /// @param size if zero, will still return a non-null pointer, but not a unique one
@@ -606,15 +609,17 @@ void *arena_alloc(Arena *arena, size_t size, bool align)
   return mem;
 }
 
-void arena_mem_free(ArenaMem mem, ArenaMem *reuse_blk)
+void arena_mem_free(ArenaMem mem)
 {
   struct consumed_blk *b = mem;
   // peel of the first block, as it is guaranteed to be ARENA_BLOCK_SIZE,
   // not a custom fix_blk
-  if (reuse_blk && *reuse_blk == NULL && b != NULL) {
-    *reuse_blk = b;
+  if (arena_reuse_blk_count < REUSE_MAX && b != NULL) {
+    struct consumed_blk *reuse_blk = b;
     b = b->prev;
-    (*reuse_blk)->prev = NULL;
+    reuse_blk->prev = arena_reuse_blk;
+    arena_reuse_blk = reuse_blk;
+    arena_reuse_blk_count++;
   }
 
   while (b) {
@@ -815,6 +820,9 @@ void free_all_mem(void)
 
   nlua_free_all_mem();
   ui_free_all_mem();
+
+  // should be last, in case earlier free functions deallocates arenas
+  arena_free_reuse_blks();
 }
 
 #endif
diff --git a/src/nvim/memory.h b/src/nvim/memory.h
index 5e37847beb..f407192331 100644
--- a/src/nvim/memory.h
+++ b/src/nvim/memory.h
@@ -52,7 +52,7 @@ typedef struct {
   size_t pos, size;
 } Arena;
 
-// inits an empty arena. use arena_start() to actually allocate space!
+// inits an empty arena.
 #define ARENA_EMPTY { .cur_blk = NULL, .pos = 0, .size = 0 }
 
 #define kv_fixsize_arena(a, v, s) \
diff --git a/src/nvim/msgpack_rpc/channel.c b/src/nvim/msgpack_rpc/channel.c
index 66fd79c692..f00c62f766 100644
--- a/src/nvim/msgpack_rpc/channel.c
+++ b/src/nvim/msgpack_rpc/channel.c
@@ -158,7 +158,7 @@ Object rpc_send_call(uint64_t id, const char *method_name, Array args, ArenaMem
     }
 
     // frame.result was allocated in an arena
-    arena_mem_free(frame.result_mem, &rpc->unpacker->reuse_blk);
+    arena_mem_free(frame.result_mem);
     frame.result_mem = NULL;
   }
 
@@ -244,7 +244,7 @@ static void parse_msgpack(Channel *channel)
         ui_client_event_raw_line(p->grid_line_event);
       } else if (p->ui_handler.fn != NULL && p->result.type == kObjectTypeArray) {
         p->ui_handler.fn(p->result.data.array);
-        arena_mem_free(arena_finish(&p->arena), &p->reuse_blk);
+        arena_mem_free(arena_finish(&p->arena));
       }
     } else if (p->type == kMessageTypeResponse) {
       ChannelCallFrame *frame = kv_last(channel->rpc.call_stack);
@@ -295,7 +295,7 @@ static void handle_request(Channel *channel, Unpacker *p, Array args)
   if (!p->handler.fn) {
     send_error(channel, p->type, p->request_id, p->unpack_error.msg);
     api_clear_error(&p->unpack_error);
-    arena_mem_free(arena_finish(&p->arena), &p->reuse_blk);
+    arena_mem_free(arena_finish(&p->arena));
     return;
   }
 
@@ -364,7 +364,7 @@ static void request_event(void **argv)
 
 free_ret:
   // e->args (and possibly result) are allocated in an arena
-  arena_mem_free(arena_finish(&e->used_mem), &channel->rpc.unpacker->reuse_blk);
+  arena_mem_free(arena_finish(&e->used_mem));
   channel_decref(channel);
   xfree(e);
   api_clear_error(&error);
diff --git a/src/nvim/msgpack_rpc/unpacker.c b/src/nvim/msgpack_rpc/unpacker.c
index c8e9fdd4c3..24480835a1 100644
--- a/src/nvim/msgpack_rpc/unpacker.c
+++ b/src/nvim/msgpack_rpc/unpacker.c
@@ -181,13 +181,11 @@ void unpacker_init(Unpacker *p)
   p->unpack_error = (Error)ERROR_INIT;
 
   p->arena = (Arena)ARENA_EMPTY;
-  p->reuse_blk = NULL;
 }
 
 void unpacker_teardown(Unpacker *p)
 {
-  arena_mem_free(p->reuse_blk, NULL);
-  arena_mem_free(arena_finish(&p->arena), NULL);
+  arena_mem_free(arena_finish(&p->arena));
 }
 
 bool unpacker_parse_header(Unpacker *p)
@@ -308,7 +306,7 @@ bool unpacker_advance(Unpacker *p)
       p->state = 10;
     } else {
       p->state = p->type == kMessageTypeResponse ? 1 : 2;
-      arena_start(&p->arena, &p->reuse_blk);
+      p->arena = (Arena)ARENA_EMPTY;
     }
   }
 
@@ -322,7 +320,7 @@ bool unpacker_advance(Unpacker *p)
       goto done;
     } else {
       // unpack other ui events using mpack_parse()
-      arena_start(&p->arena, &p->reuse_blk);
+      p->arena = (Arena)ARENA_EMPTY;
     }
   }
 
@@ -416,13 +414,13 @@ redo:
     if (p->ui_handler.fn != ui_client_event_grid_line) {
       p->state = 12;
       if (p->grid_line_event) {
-        arena_mem_free(arena_finish(&p->arena), &p->reuse_blk);
+        arena_mem_free(arena_finish(&p->arena));
         p->grid_line_event = NULL;
       }
       return true;
     } else {
       p->state = 13;
-      arena_start(&p->arena, &p->reuse_blk);
+      p->arena = (Arena)ARENA_EMPTY;
       p->grid_line_event = arena_alloc(&p->arena, sizeof *p->grid_line_event, true);
       g = p->grid_line_event;
     }
diff --git a/src/nvim/msgpack_rpc/unpacker.h b/src/nvim/msgpack_rpc/unpacker.h
index f39439be63..35048fb877 100644
--- a/src/nvim/msgpack_rpc/unpacker.h
+++ b/src/nvim/msgpack_rpc/unpacker.h
@@ -32,8 +32,6 @@ struct Unpacker {
   Error unpack_error;
 
   Arena arena;
-  // one length free-list of reusable blocks
-  ArenaMem reuse_blk;
 
   int nevents;
   int ncalls;
diff --git a/src/nvim/popupmenu.c b/src/nvim/popupmenu.c
index d392bb5a2c..f570556a29 100644
--- a/src/nvim/popupmenu.c
+++ b/src/nvim/popupmenu.c
@@ -156,7 +156,6 @@ void pum_display(pumitem_T *array, int size, int selected, bool array_changed, i
     if (pum_external) {
       if (array_changed) {
         Arena arena = ARENA_EMPTY;
-        arena_start(&arena, &ui_ext_fixblk);
         Array arr = arena_array(&arena, (size_t)size);
         for (int i = 0; i < size; i++) {
           Array item = arena_array(&arena, 4);
@@ -168,7 +167,7 @@ void pum_display(pumitem_T *array, int size, int selected, bool array_changed, i
         }
         ui_call_popupmenu_show(arr, selected, pum_win_row, cursor_col,
                                pum_anchor_grid);
-        arena_mem_free(arena_finish(&arena), &ui_ext_fixblk);
+        arena_mem_free(arena_finish(&arena));
       } else {
         ui_call_popupmenu_select(selected);
         return;
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index b471b93192..89b24e9440 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -1094,7 +1094,6 @@ void draw_tabline(void)
 static void ui_ext_tabline_update(void)
 {
   Arena arena = ARENA_EMPTY;
-  arena_start(&arena, &ui_ext_fixblk);
 
   size_t n_tabs = 0;
   FOR_ALL_TABS(tp) {
@@ -1135,7 +1134,7 @@ static void ui_ext_tabline_update(void)
   }
 
   ui_call_tabline_update(curtab->handle, tabs, curbuf->handle, buffers);
-  arena_mem_free(arena_finish(&arena), &ui_ext_fixblk);
+  arena_mem_free(arena_finish(&arena));
 }
 
 void get_trans_bufname(buf_T *buf)
diff --git a/src/nvim/tui/input.c b/src/nvim/tui/input.c
index 61a59bcf06..6afe7defe3 100644
--- a/src/nvim/tui/input.c
+++ b/src/nvim/tui/input.c
@@ -238,7 +238,7 @@ static void tinput_wait_enqueue(void **argv)
         ArenaMem res_mem = NULL;
         Object result = rpc_send_call(ui_client_channel_id, "nvim_input", args, &res_mem, &err);
         consumed = result.type == kObjectTypeInteger ? (size_t)result.data.integer : 0;
-        arena_mem_free(res_mem, NULL);
+        arena_mem_free(res_mem);
       } else {
         consumed = input_enqueue(keys);
       }
diff --git a/src/nvim/ui.c b/src/nvim/ui.c
index da671a3ad1..0126ad62b5 100644
--- a/src/nvim/ui.c
+++ b/src/nvim/ui.c
@@ -517,11 +517,10 @@ void ui_flush(void)
   }
   if (pending_mode_info_update) {
     Arena arena = ARENA_EMPTY;
-    arena_start(&arena, &ui_ext_fixblk);
     Array style = mode_style_array(&arena);
     bool enabled = (*p_guicursor != NUL);
     ui_call_mode_info_set(enabled, style);
-    arena_mem_free(arena_finish(&arena), &ui_ext_fixblk);
+    arena_mem_free(arena_finish(&arena));
     pending_mode_info_update = false;
   }
   if (pending_mode_update && !starting) {
diff --git a/src/nvim/ui.h b/src/nvim/ui.h
index 7dd2f5bce3..996b3467a6 100644
--- a/src/nvim/ui.h
+++ b/src/nvim/ui.h
@@ -47,8 +47,6 @@ enum {
 
 typedef int LineFlags;
 
-EXTERN ArenaMem ui_ext_fixblk INIT(= NULL);
-
 struct ui_t {
   bool rgb;
   bool override;  ///< Force highest-requested UI capabilities.