From nobody Thu Dec 18 20:19:26 2025 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 760941A2397 for ; Wed, 18 Dec 2024 11:16:31 +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=1734520593; cv=none; b=VA4OGV2c14yZFO7gIlZtjAX1msVh1J3p9nttDHsEEzUih/t44p2GnAimy+wgeD4FmLO3QqjsfbJAP7uL0OOEhV5Ft0qPzXEQv12vDL0hjCvnNLc0FH1pRQGBx8z+0BuKznzBNBXcHMlG1mHjRoO8X3666+N8HEbw8vCh6n1jR/w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734520593; c=relaxed/simple; bh=gXkGtxoyoXl/NMK73cExS5UnrS3URYzCFyB2LAX73YY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=n9OfLUoNNSB6CU+2DovjWE4Jc6/40H3QATyrISXiqAUouauhA0Kmc6ZZxybI+MTHpzEdA5CqJxmMhsuLLD52/GqMJ7QWCsAtse+69PPegMnWBsul/kxUXpUKj2VAI9J8UzU7PsjTkTiviFg1zJCsM6QdWdF5oGtf0N3X1x+jmyo= 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=H80C/v9N; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=d760Iv3X; 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="H80C/v9N"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="d760Iv3X" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1734520588; 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=D24xeo6QcAfcCgI6fSDs0xWo834h1otg4FtB/ux1bVA=; b=H80C/v9NSBbHrBUHTSq2KaSlc5HmEsN7Skgq0sw4+MB5WrZ14Yx0E4CHm+gNHIp0KQjdef FNHZjJnz7mq1RNn8OalNgrGQF+FsxzUbRPvtRG6WAa5/qU2yQHUfw9F8ZRFwZ1JngQjoFZ avzJ4bGD5HItdFwJ4WqqlKh3g0NAZDvhTfjD4X9OgjCquGimBkX96qooneSB5jFE7Y5Sja 87hQarsu0iy7JBHG2KlqO5KArx+NMGU5imUnrJRHEs7iqLMlpUwwQyh5pc4IyjLUw1THsj OpVhu8AW/AU/rxRcFez+jKHbIHf/0BZAu/oLNMi8JpHNCr1enUDOS+NhNn9TNw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1734520588; 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=D24xeo6QcAfcCgI6fSDs0xWo834h1otg4FtB/ux1bVA=; b=d760Iv3XFK7Hk2aFNIBeCOijmXsmLqAyfaBt2yAybjJGtEXl2fYV0SIbwquEhUwRz+69f3 22KgJPQByrSt5IDg== 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 v6 11/15] futex: Resize local futex hash table based on number of threads. Date: Wed, 18 Dec 2024 12:09:49 +0100 Message-ID: <20241218111618.268028-12-bigeasy@linutronix.de> In-Reply-To: <20241218111618.268028-1-bigeasy@linutronix.de> References: <20241218111618.268028-1-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. Signed-off-by: Sebastian Andrzej Siewior --- include/linux/futex.h | 12 ------------ kernel/fork.c | 4 +--- kernel/futex/core.c | 25 ++++++++++++++++++++++--- 3 files changed, 23 insertions(+), 18 deletions(-) diff --git a/include/linux/futex.h b/include/linux/futex.h index 3ced01a9c5218..403b54526a081 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_hash_bucket) - 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 95d38709fde10..7364fa5f2872a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2134,9 +2134,7 @@ 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 44e16f033a4dd..95a177f0c5d68 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -1370,8 +1370,8 @@ 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 @@ -1412,7 +1412,26 @@ 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_hash_bucket_private *hb_p; + + if (!current->mm) + return 0; + + scoped_guard(rcu) { + threads =3D get_nr_threads(current); + hb_p =3D rcu_dereference(current->mm->futex_hash_bucket); + if (hb_p) + current_buckets =3D hb_p->hash_mask + 1; + } + + 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 2.45.2