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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id w1-20020a81a201000000b005837633d9cbsm1033602ywg.64.2023.10.05.22.42.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Oct 2023 22:42:19 -0700 (PDT) Date: Thu, 5 Oct 2023 22:42:17 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: "Chen, Tim C" cc: Hugh Dickins , Andrew Morton , Dave Chinner , "Darrick J. Wong" , Christian Brauner , Carlos Maiolino , Chuck Lever , Jan Kara , Matthew Wilcox , Johannes Weiner , Axel Rasmussen , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" Subject: RE: [PATCH 8/8] shmem,percpu_counter: add _limited_add(fbc, limit, amount) In-Reply-To: Message-ID: <17877ef1-8aac-378b-94-af5afa2793ae@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: jzofscfyb6oqu6uqgnhdtc7yfuw56kmt X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 42ADC80013 X-Rspam-User: X-HE-Tag: 1696570941-342701 X-HE-Meta: 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 cIexswOV sYgbU9608mFRvJeMbmpKgDQ//1Hrn1z6Dr/nS4ttd9tzVzHEEMixRhFNdB7IM0I05E0Sch4FXr5glaYiIs2XgxpdcgkXKCdrxX+WvZcE67Z608iHeEuqJzMfQ6E/qZCKyqiUnWKpHvhVYeLMBdPt9AYaf/ASrPjEa73HwE/XQ+uTyVsB5cBl2hpg+Zd1Luwn+qAc3FvAniQpjF7gH+NHS3/3nOrntXpyQpuLW+Pb+bPwA550uaq8o08LxJ2SHCKvK5fl82qJq0Vb/BnjpYDNkHGbk01roSv4QDUCQK/6y4KSuIuevXSSIMcYjDAJD522gzDeeTaPp1T9Gy9Swod/axA3raT81agVStvm37X8Mqey4ha+kvhI+OrFAC/4jIPiDRaP7RssXDj8EbAbB29+OEWIY3jXz1TkreNrZUvUIKbW8C+uaineGMCQkKJe2z0pXsCbM2vqQnwI1NZg= 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 Thu, 5 Oct 2023, Chen, Tim C wrote: > >--- a/lib/percpu_counter.c > >+++ b/lib/percpu_counter.c > >@@ -278,6 +278,59 @@ int __percpu_counter_compare(struct > >percpu_counter *fbc, s64 rhs, s32 batch) } > >EXPORT_SYMBOL(__percpu_counter_compare); > > > >+/* > >+ * Compare counter, and add amount if the total is within limit. > >+ * Return true if amount was added, false if it would exceed limit. > >+ */ > >+bool __percpu_counter_limited_add(struct percpu_counter *fbc, > >+ s64 limit, s64 amount, s32 batch) { > >+ s64 count; > >+ s64 unknown; > >+ unsigned long flags; > >+ bool good; > >+ > >+ if (amount > limit) > >+ return false; > >+ > >+ local_irq_save(flags); > >+ unknown = batch * num_online_cpus(); > >+ count = __this_cpu_read(*fbc->counters); > >+ > >+ /* Skip taking the lock when safe */ > >+ if (abs(count + amount) <= batch && > >+ fbc->count + unknown <= limit) { > >+ this_cpu_add(*fbc->counters, amount); > >+ local_irq_restore(flags); > >+ return true; > >+ } > >+ > >+ raw_spin_lock(&fbc->lock); > >+ count = fbc->count + amount; > >+ > > Perhaps we can fast path the case where for sure > we will exceed limit? > > if (fbc->count + amount - unknown > limit) > return false; Thanks, that sounds reasonable: I'll try to add something like that - but haven't thought about it carefully enough yet (too easy for me to overlook some negative case which messes everything up). Hugh