From nobody Wed Dec 17 19:59:43 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 D171B1A23A9 for ; Tue, 25 Feb 2025 17:09:31 +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=1740503374; cv=none; b=tiAdDzTapQ7TyUIA/kJ/jyqtCo5zJ7NP7VC29obugTqrHp0HA3JOtW92jdFTb0HXuUgXV89sUmg8KZcXEMhu1CHWhunfZc5PvyP9JFDjzddiXTVTFQ9+IDR9VPlaEMSdMF04g7wVe4MHxK0bKfBzedhswJ8E8PmmwY6b8JZHCpw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740503374; c=relaxed/simple; bh=8FFO6bFPGwyY0+Xl6fvMWNJIoLX7x/wmhWfnnYAgvQw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lleUR8JtQPAzy8g5/yUUf8eZ2cuowNQLDBu6JfLyLeW5pEDoXzcvfeCczitqsbam+5qdoQUyj07tkb/dYuSnBV+ZwdF7A/aAeBMibZEiT8h8ugDCvYMQtJ0n75MzoDQO9LwNjwy6gwUnOcGDJbudtzF29mH0tkz7t0P3sjj1a2o= 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=0/OgES9X; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=jEqTkPGN; 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="0/OgES9X"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="jEqTkPGN" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1740503364; 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=YX0O8wuELXX5Vdc+92JPzZgR8pAmCG7s5ghLTgE+/8A=; b=0/OgES9XvkRg6FQDFk0MG+GCGCqmZFXTZZdvEOKFE4u+tzOj6mfcfWObDLnD3+a6YbEHDt LU0KXDV8Ii/Wjg+77yxS7bhRYwfxE9YRAGIffFWDyUAb1PDdT9IIIXGOoWbIDGJDFlzhmk RhQUBjaPlBXIsJ5ZO/JQXPHgq7KZ3kfg74kWc3PSg+DexgxyhjN9TzF8it9mA0DYG/tBsG 9whV4M29iwqc1u9U9OMRPUPOKg15InOVjdr97iT/y/S4fJzIFLBlMz0Z5vFsmMij53UY6R hRYvjsHjBUt5DTEH8lhNNltbrNhy+GPOja+UlIoDCfJKWARLtJi1+Qd6V6gR8g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740503364; 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=YX0O8wuELXX5Vdc+92JPzZgR8pAmCG7s5ghLTgE+/8A=; b=jEqTkPGNeZxldgoz/YkjeCmWgaTCJy4WBMSUNyYVbjh42D7whPa6Obd9Pc/Ig3LU1KaPkZ iIB5SD9vDjS0/aCQ== 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 v9 10/11] futex: Resize local futex hash table based on number of threads. Date: Tue, 25 Feb 2025 18:09:13 +0100 Message-ID: <20250225170914.289358-11-bigeasy@linutronix.de> In-Reply-To: <20250225170914.289358-1-bigeasy@linutronix.de> References: <20250225170914.289358-1-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 but don't exceed the number of online CPUs. 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 additional members for private hash resize have been removed in order to save memory on mm_struct and avoid any additional memory consumption. If we really do this, then I would re-arrange the code structure in the previous patches to limit the ifdefs. The alternatives would be to limit the buckets allocated in futex_hash_allocate_default() to 2. Avoiding futex_hash_allocate_default() but allowing PR_FUTEX_HASH_SET_SLOTS to work would require to hold mm_struct::futex_hash_lock in exit_pi_state_list() and futex_wait_multiple_setup() that private does not appear during these operations (which is currently ensured by holding a reference). Signed-off-by: Sebastian Andrzej Siewior --- include/linux/futex.h | 21 +++++++-------- include/linux/mm_types.h | 2 +- kernel/fork.c | 4 +-- kernel/futex/core.c | 57 +++++++++++++++++++++++++++++++++++++--- kernel/futex/futex.h | 8 ++++++ 5 files changed, 73 insertions(+), 19 deletions(-) diff --git a/include/linux/futex.h b/include/linux/futex.h index bfb38764bac7a..77821a78059f2 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -78,6 +78,13 @@ void futex_exec_release(struct task_struct *tsk); long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, u32 __user *uaddr2, u32 val2, u32 val3); int futex_hash_prctl(unsigned long arg2, unsigned long arg3); + +#ifdef CONFIG_BASE_SMALL +static inline int futex_hash_allocate_default(void) { return 0; } +static inline void futex_hash_free(struct mm_struct *mm) { } +static inline void futex_mm_init(struct mm_struct *mm) { } +#else /* !CONFIG_BASE_SMALL */ + int futex_hash_allocate_default(void); void futex_hash_free(struct mm_struct *mm); =20 @@ -87,14 +94,9 @@ 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; -} +#endif /* CONFIG_BASE_SMALL */ =20 -#else +#else /* !CONFIG_FUTEX */ static inline void futex_init_task(struct task_struct *tsk) { } static inline void futex_exit_recursive(struct task_struct *tsk) { } static inline void futex_exit_release(struct task_struct *tsk) { } @@ -116,11 +118,6 @@ 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/include/linux/mm_types.h b/include/linux/mm_types.h index 19abbc870e0a9..72e68de850745 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -937,7 +937,7 @@ struct mm_struct { */ seqcount_t mm_lock_seq; #endif -#ifdef CONFIG_FUTEX +#if defined(CONFIG_FUTEX) && !defined(CONFIG_BASE_SMALL) struct mutex futex_hash_lock; struct futex_private_hash __rcu *futex_phash; struct futex_private_hash *futex_phash_new; 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 4d9ee3bcaa6d0..6d375b9407c85 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -138,6 +138,7 @@ static struct futex_hash_bucket *futex_hash_private(uni= on futex_key *key, return &fhb[hash & hash_mask]; } =20 +#ifndef CONFIG_BASE_SMALL static void futex_rehash_current_users(struct futex_private_hash *old, struct futex_private_hash *new) { @@ -256,6 +257,14 @@ static struct futex_private_hash *futex_get_private_hb= (union futex_key *key) return futex_get_private_hash(); } =20 +#else + +static struct futex_private_hash *futex_get_private_hb(union futex_key *ke= y) +{ + return NULL; +} +#endif + /** * futex_hash - Return the hash bucket in the global or local hash * @key: Pointer to the futex key for which the hash is calculated @@ -279,6 +288,7 @@ struct futex_hash_bucket *__futex_hash(union futex_key = *key) return &futex_queues[hash & (futex_hashsize - 1)]; } =20 +#ifndef CONFIG_BASE_SMALL bool futex_put_private_hash(struct futex_private_hash *hb_p) { bool released; @@ -315,6 +325,7 @@ void futex_hash_put(struct futex_hash_bucket *hb) return; futex_put_private_hash(hb_p); } +#endif =20 /** * futex_setup_timer - set up the sleeping hrtimer. @@ -1366,12 +1377,15 @@ void futex_exit_release(struct task_struct *tsk) static void futex_hash_bucket_init(struct futex_hash_bucket *fhb, struct futex_private_hash *hb_p) { +#ifndef CONFIG_BASE_SMALL fhb->hb_p =3D hb_p; +#endif atomic_set(&fhb->waiters, 0); plist_head_init(&fhb->chain); spin_lock_init(&fhb->lock); } =20 +#ifndef CONFIG_BASE_SMALL void futex_hash_free(struct mm_struct *mm) { struct futex_private_hash *hb_p; @@ -1406,8 +1420,8 @@ 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 @@ -1449,7 +1463,31 @@ 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 min_t(unsigned int, get_nr_threads(current), num_online_cpus= ()); + hb_p =3D rcu_dereference(current->mm->futex_phash); + if (hb_p) + current_buckets =3D hb_p->hash_mask + 1; + } + + /* + * 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) @@ -1463,6 +1501,19 @@ static int futex_hash_get_slots(void) return 0; } =20 +#else + +static int futex_hash_allocate(unsigned int hash_slots) +{ + return -EINVAL; +} + +static int futex_hash_get_slots(void) +{ + return 0; +} +#endif + int futex_hash_prctl(unsigned long arg2, unsigned long arg3) { int ret; diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h index 973efcca2e01b..d1149739f3110 100644 --- a/kernel/futex/futex.h +++ b/kernel/futex/futex.h @@ -205,10 +205,18 @@ futex_setup_timer(ktime_t *time, struct hrtimer_sleep= er *timeout, int flags, u64 range_ns); =20 extern struct futex_hash_bucket *__futex_hash(union futex_key *key); +#ifdef CONFIG_BASE_SMALL +static inline void futex_hash_get(struct futex_hash_bucket *hb) { } +static inline void futex_hash_put(struct futex_hash_bucket *hb) { } +static inline struct futex_private_hash *futex_get_private_hash(void) { re= turn NULL; } +static inline bool futex_put_private_hash(struct futex_private_hash *hb_p)= { return false; } + +#else /* !CONFIG_BASE_SMALL */ extern void futex_hash_get(struct futex_hash_bucket *hb); extern void futex_hash_put(struct futex_hash_bucket *hb); extern struct futex_private_hash *futex_get_private_hash(void); extern bool futex_put_private_hash(struct futex_private_hash *hb_p); +#endif =20 DEFINE_CLASS(hb, struct futex_hash_bucket *, if (_T) futex_hash_put(_T), --=20 2.47.2