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[2003:cb:c707:6e00:ff02:ec7a:ded5:ec1e]) by smtp.gmail.com with ESMTPSA id g19-20020a05600c4ed300b003d978f8f255sm2202586wmq.27.2023.01.05.00.44.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Jan 2023 00:44:17 -0800 (PST) Message-ID: Date: Thu, 5 Jan 2023 09:44:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 2/3] mm/mprotect: Use long for page accountings and retval To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Kravetz , Muchun Song , Nadav Amit , Andrea Arcangeli , James Houghton , Axel Rasmussen , Andrew Morton References: <20230104225207.1066932-1-peterx@redhat.com> <20230104225207.1066932-3-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230104225207.1066932-3-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: C5ED84000C X-Rspamd-Server: rspam01 X-Stat-Signature: 7gmzf75ferqj5ue6jt6rqgka5c77a3dw X-HE-Tag: 1672908260-233792 X-HE-Meta: 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 pB9D0PI5 srUqveA/9SvD/9yHFHAKCm5fzrN+DF4mtOYzXjc07f0bkXCBXvAzBZRREsScwGdojEdBBI78zWWVnfZQ3BodYnJDMzb0Pp2aHotYEthGTWvcH/LrbZ1VyarbUCMgmt5gR+/OYQhjshCNzktUCu3wDM+IQ2WW4bsFsqizaK8yDAPMVq7uzjZaYQ4is/01+VIW8ybuT1O+e1NhgjJ4fubjf2fw/uw== 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 04.01.23 23:52, Peter Xu wrote: > Switch to use type "long" for page accountings and retval across the whole > procedure of change_protection(). > > The change should have shrinked the possible maximum page number to be half > comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on any > system either because the maximum possible pages touched by change > protection should be ULONG_MAX / PAGE_SIZE. Yeah, highly unlikely. > > Two reasons to switch from "unsigned long" to "long": > > 1. It suites better on count_vm_numa_events(), whose 2nd parameter takes > a long type. > > 2. It paves way for returning negative (error) values in the future. > > Currently the only caller that consumes this retval is change_prot_numa(), > where the unsigned long was converted to an int. Since at it, touching up > the numa code to also take a long, so it'll avoid any possible overflow too > during the int-size convertion. I'm wondering if we should just return the number of changed pages via a separate pointer and later using an int for returning errors -- when touching this interface already. Only who's actually interested in the number of pages would pass a pointer to an unsigned long (NUMA). And code that expects that there never ever are failures (mprotect, NUMA) could simply check for WARN_ON_ONCE(ret). I assume you evaluated that option as well, what was your conclusion? -- Thanks, David / dhildenb