linux-kernel - [RFC PATCH v2 3/4] futex: Use the task local hashmap.

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Message-ID: <20241028121921.1264150-4-bigeasy@linutronix.de>
Date: Mon, 28 Oct 2024 13:13:57 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: André Almeida <andrealmeid@...lia.com>,
	Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Valentin Schneider <vschneid@...hat.com>,
	Waiman Long <longman@...hat.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [RFC PATCH v2 3/4] futex: Use the task local hashmap.

Use the hashlocal hashmap if provided.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/futex/core.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 14e4cb5ccd722..3ef4cbd5cfa72 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -108,18 +108,33 @@ late_initcall(fail_futex_debugfs);
 
 #endif /* CONFIG_FAIL_FUTEX */
 
+static inline bool futex_key_is_private(union futex_key *key)
+{
+	/*
+	 * Relies on get_futex_key() to set either bit for shared
+	 * futexes -- see comment with union futex_key.
+	 */
+	return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED));
+}
+
 /**
  * futex_hash - Return the hash bucket in the global hash
  * @key:	Pointer to the futex key for which the hash is calculated
  *
  * We hash on the keys returned from get_futex_key (see below) and return the
- * corresponding hash bucket in the global hash.
+ * corresponding hash bucket in the global hash. If the FUTEX is private and
+ * a local hash table is privated then this one is used.
  */
 struct futex_hash_bucket *futex_hash(union futex_key *key)
 {
+	struct futex_hash_bucket *fhb;
 	u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
 			  key->both.offset);
 
+	fhb = current->signal->futex_hash_bucket;
+	if (fhb && futex_key_is_private(key))
+		return &fhb[hash & current->signal->futex_hash_mask];
+
 	return &futex_queues[hash & (futex_hashsize - 1)];
 }
 
-- 
2.45.2