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[209.85.208.46]) by smtp.gmail.com with ESMTPSA id c19-20020a170906155300b0093ebc654f78sm6569282ejd.25.2023.03.29.09.50.56 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Mar 2023 09:50:56 -0700 (PDT) Received: by mail-ed1-f46.google.com with SMTP id i5so66153935eda.0 for ; Wed, 29 Mar 2023 09:50:56 -0700 (PDT) X-Received: by 2002:a17:906:eec7:b0:93e:186f:ea0d with SMTP id wu7-20020a170906eec700b0093e186fea0dmr9808123ejb.15.1680108655974; Wed, 29 Mar 2023 09:50:55 -0700 (PDT) MIME-Version: 1.0 References: <20230329053149.3976378-1-mcgrof@kernel.org> <20230329053149.3976378-5-mcgrof@kernel.org> <20230329072112.GG4253@hirez.programming.kicks-ass.net> <20230329091935.GP4253@hirez.programming.kicks-ass.net> In-Reply-To: <20230329091935.GP4253@hirez.programming.kicks-ass.net> From: Linus Torvalds Date: Wed, 29 Mar 2023 09:50:39 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 4/7] sempahore: add a helper for a concurrency limiter To: Peter Zijlstra Cc: Luis Chamberlain , david@redhat.com, patches@lists.linux.dev, linux-modules@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, pmladek@suse.com, petr.pavlu@suse.com, prarit@redhat.com, gregkh@linuxfoundation.org, rafael@kernel.org, christophe.leroy@csgroup.eu, tglx@linutronix.de, song@kernel.org, rppt@kernel.org, willy@infradead.org, vbabka@suse.cz, mhocko@suse.com, dave.hansen@linux.intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 820A418000D X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: nq8tfuy64kkkk8dez3s4ya3sw9bzcayq X-HE-Tag: 1680108659-823539 X-HE-Meta: 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 LHzScAr1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 29, 2023 at 2:19=E2=80=AFAM Peter Zijlstra wrote: > > Arguably DEFINE_SEMAPHORE() should have the argument, as binary > semaphores are a special case, but then we gotta go and fix up all > users. Using semaphores for just pure mutual exclusion used to be *the* most common use of it, which is why we didn't have an argument. Then we got the mutexes, and now semaphores are almost entirely a legacy th= ing. I think we should just make DEFINE_SEMAPHORE() take the number, and people who want a mutex should either put in the "1", or they should just use a mutex. > /me git-greps a little.. Hmm, not too bad. > > How's this? I'd actually prefer to not have that DEFINE_BINARY_SEMAPHORE() at all. It really shouldn't exist in this day and age. It's not even less typing, ie static DEFINE_SEMAPHORE(efivars_lock, 1); is actually shorter than static DEFINE_BINARY_SEMAPHORE(efivars_lock); And what you actually *want* is static DEFINE_MUTEX(efivars_lock); and converting the up/down to mutex_unlock/mutex_lock. So let's just make it clear that the only reason to use semaphores these days is for counting semaphores, and just make DEFINE_SEMAPHORE() take the number. Strangely, sema_init() already does that, but I guess that's because some people really *do* use semaphores for concurrency control (ie I see things like sema_init(&dc->in_flight, 64); which is clearly using a semaphore in that very traditional way). So ack on your patch, but don't bother with DEFINE_BINARY_SEMAPHORE(). Linus