From nobody Tue Feb 10 16:18:44 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FB652066ED for ; Mon, 3 Feb 2025 13:59:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738591194; cv=none; b=plhdqo3InfZcm7gRKoW3nAL2xet/sjO6NzJJ4LzAXNS/Von3ODjFwUdIZ+GEABRM5lyyemdch2ceLbp9Ol99PqH8ZtdXn1FvisZEiKpQ1d6EfZyOgrRIbVjsePCIcrGgOatS+sJn1TlPVEzzHniumoOCRwfrQIgWG/DoEuw8Qv8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738591194; c=relaxed/simple; bh=At0iobiar2kYsDUJScEyR9TMwWbMFo3Vzl5kX1JCPYY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Jx3yFEuh9i4dWciZH7Zm2jTK329MwyoOQd50in0TzP5/P8bcfy9OcSYSxLe/bFGsiLDU/e9AnI+/LHF39wvQvMvirav+McHJKwbdxZSyB+NXQah/Z0l8L8DyAQlTBfRWOW69a3aLSsmyYbvbRRIyfvo2vnxOCcgh+zy183i0WgI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=1lJSq7mX; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=/wzqmem8; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="1lJSq7mX"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="/wzqmem8" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1738591188; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fa74DZfXPqAvHSMVYpF3I4XvhkatGI0nWl7rzvRsR1w=; b=1lJSq7mXVlT5TEdN0+T0PW8YHc+RCaAALIuYM/Qdk5Of9Bzg6B6SvCpRdbbPRaHLrMdKOS UjXYtKF1yv9H1XoYakHenG8KGUmSTFbnG2eBcs+Bm06CBSY5hJ0WTfcHXwSQqb/5oc3yri bo6g4EStNvAfMRce77e/pOz7Yv8vlF5YVcoHR3TUGfJhbS5UzrmZTlgRlEKxIivhJenFeT orLWGEE89EQJvIsQVdde1YG9TiYbXape9TdA/EZHE+FbxsoY/vl0ToYZgtmq8JCkvgvj5d 794jXCVYVjEpiOtZNkoJZLdGfTigmIUGP13s0+SMILxcw0cjXBKo4spiJ2ESbg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1738591188; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fa74DZfXPqAvHSMVYpF3I4XvhkatGI0nWl7rzvRsR1w=; b=/wzqmem8sQH6iVu6jPrN7houDx6dfAVXdFrOHLDViLgzJV2ZmnPiqF3GouE/g0I7hOhvpA yGjUh97/Cxl8WuCA== To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Andr=C3=A9=20Almeida?= , Darren Hart , Davidlohr Bueso , Ingo Molnar , Juri Lelli , Peter Zijlstra , Thomas Gleixner , Valentin Schneider , Waiman Long , Sebastian Andrzej Siewior Subject: [PATCH v8 13/15] futex: Resize local futex hash table based on number of threads. Date: Mon, 3 Feb 2025 14:59:33 +0100 Message-ID: <20250203135935.440018-14-bigeasy@linutronix.de> In-Reply-To: <20250203135935.440018-1-bigeasy@linutronix.de> References: <20250203135935.440018-1-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Automatically size the local hash based on the number of threads. The logic tries to allocate between 16 and futex_hashsize (the default for the system wide hash bucket) and uses 4 * number-of-threads. On CONFIG_BASE_SMALL configs the suggested size is always 2. Signed-off-by: Sebastian Andrzej Siewior --- include/linux/futex.h | 12 ------------ kernel/fork.c | 4 +--- kernel/futex/core.c | 34 +++++++++++++++++++++++++++++++--- 3 files changed, 32 insertions(+), 18 deletions(-) diff --git a/include/linux/futex.h b/include/linux/futex.h index bfb38764bac7a..6469aeb76a150 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -87,13 +87,6 @@ static inline void futex_mm_init(struct mm_struct *mm) mutex_init(&mm->futex_hash_lock); } =20 -static inline bool futex_hash_requires_allocation(void) -{ - if (current->mm->futex_phash) - return false; - return true; -} - #else static inline void futex_init_task(struct task_struct *tsk) { } static inline void futex_exit_recursive(struct task_struct *tsk) { } @@ -116,11 +109,6 @@ static inline int futex_hash_allocate_default(void) static inline void futex_hash_free(struct mm_struct *mm) { } static inline void futex_mm_init(struct mm_struct *mm) { } =20 -static inline bool futex_hash_requires_allocation(void) -{ - return false; -} - #endif =20 #endif diff --git a/kernel/fork.c b/kernel/fork.c index 824cc55d32ece..5e15e5b24f289 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2142,9 +2142,7 @@ static bool need_futex_hash_allocate_default(u64 clon= e_flags) { if ((clone_flags & (CLONE_THREAD | CLONE_VM)) !=3D (CLONE_THREAD | CLONE_= VM)) return false; - if (!thread_group_empty(current)) - return false; - return futex_hash_requires_allocation(); + return true; } =20 /* diff --git a/kernel/futex/core.c b/kernel/futex/core.c index e1bf43f7eb277..9a12dccb1c995 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -1411,8 +1411,8 @@ static int futex_hash_allocate(unsigned int hash_slot= s) hash_slots =3D 16; if (hash_slots < 2) hash_slots =3D 2; - if (hash_slots > 131072) - hash_slots =3D 131072; + if (hash_slots > futex_hashsize) + hash_slots =3D futex_hashsize; if (!is_power_of_2(hash_slots)) hash_slots =3D rounddown_pow_of_two(hash_slots); =20 @@ -1454,7 +1454,35 @@ static int futex_hash_allocate(unsigned int hash_slo= ts) =20 int futex_hash_allocate_default(void) { - return futex_hash_allocate(0); + unsigned int threads, buckets, current_buckets =3D 0; + struct futex_private_hash *hb_p; + + if (!current->mm) + return 0; + + scoped_guard(rcu) { + threads =3D get_nr_threads(current); + hb_p =3D rcu_dereference(current->mm->futex_phash); + if (hb_p) + current_buckets =3D hb_p->hash_mask + 1; + } + + if (IS_ENABLED(CONFIG_BASE_SMALL)) { + buckets =3D 2; + + } else { + /* + * The default allocation will remain within + * 16 <=3D threads * 4 <=3D global hash size + */ + buckets =3D roundup_pow_of_two(4 * threads); + buckets =3D max(buckets, 16); + buckets =3D min(buckets, futex_hashsize); + } + if (current_buckets >=3D buckets) + return 0; + + return futex_hash_allocate(buckets); } =20 static int futex_hash_get_slots(void) --=20 2.47.2