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[73.224.175.84]) by smtp.gmail.com with ESMTPSA id 00721157ae682-70f8ac0f42esm31529627b3.68.2025.06.04.14.46.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jun 2025 14:46:59 -0700 (PDT) Date: Wed, 4 Jun 2025 17:46:59 -0400 From: Yury Norov To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Rasmus Villemoes , John Stultz , Thomas Gleixner , Stephen Boyd Subject: Re: [PATCH 1/3] bitmap: generalize node_random() Message-ID: References: <20250604212125.25656-1-yury.norov@gmail.com> <20250604212125.25656-2-yury.norov@gmail.com> <20250604143442.37635ce63e50a7425a390c2e@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250604143442.37635ce63e50a7425a390c2e@linux-foundation.org> On Wed, Jun 04, 2025 at 02:34:42PM -0700, Andrew Morton wrote: > On Wed, 4 Jun 2025 17:21:21 -0400 Yury Norov wrote: > > > Generalize node_random and make it available to general bitmaps and > > cpumasks users. > > Seems sensible. > > > --- a/lib/find_bit.c > > +++ b/lib/find_bit.c > > > > +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: > > + return find_first_bit(addr, size); > > Is the `1' special case useful? The `default' case should still work OK? find_first_bit() is faster that find_nth_bit(), so this is a performance optimization. See 3e061d924fe9c7b4 ("lib/nodemask: optimize node_random for nodemask with single NUMA node"). > > + default: > > + return find_nth_bit(addr, size, get_random_u32_below(w)); > > + } > > +} > > +EXPORT_SYMBOL(find_random_bit); > > Some kerneldoc, please? Indeed, will send v2. > Of course, the hard-coding of get_random_u32_below() might be > unsuitable for some future potential callers but we can deal with that > if it ever occurs. Can you please elaborate? Thanks, Yury