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[73.224.175.84]) by smtp.gmail.com with ESMTPSA id 00721157ae682-710f98afb31sm10052557b3.24.2025.06.08.12.45.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Jun 2025 12:45:39 -0700 (PDT) From: Yury Norov To: linux-kernel@vger.kernel.org, Yury Norov , Rasmus Villemoes , John Stultz , Thomas Gleixner , Stephen Boyd , Andrew Morton Subject: [PATCH 1/3] bitmap: generalize node_random() Date: Sun, 8 Jun 2025 15:45:33 -0400 Message-ID: <20250608194536.28130-2-yury.norov@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250608194536.28130-1-yury.norov@gmail.com> References: <20250608194536.28130-1-yury.norov@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Yury Norov [NVIDIA]" Generalize node_random() and make it available to general bitmaps and cpumasks users. Notice, find_first_bit() is generally faster than find_nth_bit(), and we employ it when there's a single set bit in the bitmap. See commit 3e061d924fe9c7b4 ("lib/nodemask: optimize node_random for nodemask with single NUMA node"). Signed-off-by: Yury Norov [NVIDIA] --- include/linux/find.h | 2 ++ include/linux/nodemask.h | 17 +---------------- lib/find_bit.c | 24 ++++++++++++++++++++++++ 3 files changed, 27 insertions(+), 16 deletions(-) diff --git a/include/linux/find.h b/include/linux/find.h index 5a2c267ea7f9..98c61838002c 100644 --- a/include/linux/find.h +++ b/include/linux/find.h @@ -44,6 +44,8 @@ unsigned long _find_next_bit_le(const unsigned long *addr, unsigned long size, unsigned long offset); #endif +unsigned long find_random_bit(const unsigned long *addr, unsigned long size); + #ifndef find_next_bit /** * find_next_bit - find the next set bit in a memory region diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h index f08ae71585fa..d49f3bd3e20b 100644 --- a/include/linux/nodemask.h +++ b/include/linux/nodemask.h @@ -91,7 +91,6 @@ #include #include #include -#include extern nodemask_t _unused_nodemask_arg_; @@ -492,21 +491,7 @@ static __always_inline int num_node_state(enum node_states state) static __always_inline int node_random(const nodemask_t *maskp) { #if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1) - int w, bit; - - w = nodes_weight(*maskp); - switch (w) { - case 0: - bit = NUMA_NO_NODE; - break; - case 1: - bit = first_node(*maskp); - break; - default: - bit = find_nth_bit(maskp->bits, MAX_NUMNODES, get_random_u32_below(w)); - break; - } - return bit; + return find_random_bit(maskp->bits, MAX_NUMNODES); #else return 0; #endif diff --git a/lib/find_bit.c b/lib/find_bit.c index 06b6342aa3ae..d4b5a29e3e72 100644 --- a/lib/find_bit.c +++ b/lib/find_bit.c @@ -18,6 +18,7 @@ #include #include #include +#include /* * Common helper for find_bit() function family @@ -291,3 +292,26 @@ EXPORT_SYMBOL(_find_next_bit_le); #endif #endif /* __BIG_ENDIAN */ + +/** + * find_random_bit - find a set bit at random position + * @addr: The address to base the search on + * @size: The bitmap size in bits + * + * Returns: a position of a random set bit; >= @size otherwise + */ +unsigned long find_random_bit(const unsigned long *addr, unsigned long size) +{ + int w = bitmap_weight(addr, size); + + switch (w) { + case 0: + return size; + case 1: + /* Performance trick for single-bit bitmaps */ + return find_first_bit(addr, size); + default: + return find_nth_bit(addr, size, get_random_u32_below(w)); + } +} +EXPORT_SYMBOL(find_random_bit); -- 2.43.0