From 8d8379da443f46dc976252b968cb9ca8e63ec974 Mon Sep 17 00:00:00 2001
From: Qi Wang <interwq@gwu.edu>
Date: Thu, 2 May 2024 12:53:42 -0700
Subject: [PATCH] Fix background_thread creation for the oversize_arena.

Bypassing background thread creation for the oversize_arena used to be an
optimization since that arena had eager purging.  However #2466 changed the
purging policy for the oversize_arena -- specifically it switched to the default
decay time when background_thread is enabled.

This issue is noticable when the number of arenas is low: whenever the total #
of arenas is <= 4 (which is the default max # of background threads), in which
case the purging will be stalled since no background thread is created for the
oversize_arena.
---
 include/jemalloc/internal/arena_externs.h |  1 -
 src/arena.c                               |  8 --------
 src/ctl.c                                 | 11 -----------
 src/jemalloc.c                            |  7 ++-----
 4 files changed, 2 insertions(+), 25 deletions(-)

diff --git a/include/jemalloc/internal/arena_externs.h b/include/jemalloc/internal/arena_externs.h
index f91bd888..3d0329fc 100644
--- a/include/jemalloc/internal/arena_externs.h
+++ b/include/jemalloc/internal/arena_externs.h
@@ -103,7 +103,6 @@ void arena_nthreads_inc(arena_t *arena, bool internal);
 void arena_nthreads_dec(arena_t *arena, bool internal);
 arena_t *arena_new(tsdn_t *tsdn, unsigned ind, const arena_config_t *config);
 bool arena_init_huge(arena_t *a0);
-bool arena_is_huge(unsigned arena_ind);
 arena_t *arena_choose_huge(tsd_t *tsd);
 bin_t *arena_bin_choose(tsdn_t *tsdn, arena_t *arena, szind_t binind,
     unsigned *binshard);
diff --git a/src/arena.c b/src/arena.c
index 8c87d67f..1e5289e4 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -1867,14 +1867,6 @@ arena_init_huge(arena_t *a0) {
 	return huge_enabled;
 }
 
-bool
-arena_is_huge(unsigned arena_ind) {
-	if (huge_arena_ind == 0) {
-		return false;
-	}
-	return (arena_ind == huge_arena_ind);
-}
-
 bool
 arena_boot(sc_data_t *sc_data, base_t *base, bool hpa) {
 	arena_dirty_decay_ms_default_set(opt_dirty_decay_ms);
diff --git a/src/ctl.c b/src/ctl.c
index 37b69576..3b90aa15 100644
--- a/src/ctl.c
+++ b/src/ctl.c
@@ -2985,17 +2985,6 @@ arena_i_decay_ms_ctl_impl(tsd_t *tsd, const size_t *mib, size_t miblen,
 			ret = EINVAL;
 			goto label_return;
 		}
-		if (arena_is_huge(arena_ind) && *(ssize_t *)newp > 0) {
-			/*
-			 * By default the huge arena purges eagerly.  If it is
-			 * set to non-zero decay time afterwards, background
-			 * thread might be needed.
-			 */
-			if (background_thread_create(tsd, arena_ind)) {
-				ret = EFAULT;
-				goto label_return;
-			}
-		}
 
 		if (arena_decay_ms_set(tsd_tsdn(tsd), arena, state,
 		    *(ssize_t *)newp)) {
diff --git a/src/jemalloc.c b/src/jemalloc.c
index 390912ba..77407714 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -430,11 +430,8 @@ arena_new_create_background_thread(tsdn_t *tsdn, unsigned ind) {
 	if (ind == 0) {
 		return;
 	}
-	/*
-	 * Avoid creating a new background thread just for the huge arena, which
-	 * purges eagerly by default.
-	 */
-	if (have_background_thread && !arena_is_huge(ind)) {
+
+	if (have_background_thread) {
 		if (background_thread_create(tsdn_tsd(tsdn), ind)) {
 			malloc_printf("<jemalloc>: error in background thread "
 				      "creation for arena %u. Abort.\n", ind);