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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1 Subject: Re: [RFC 3/8] mm: Avoid using set_page_count() in set_page_recounted() Content-Language: en-US To: Pasha Tatashin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-m68k@lists.linux-m68k.org, anshuman.khandual@arm.com, willy@infradead.org, akpm@linux-foundation.org, william.kucharski@oracle.com, mike.kravetz@oracle.com, vbabka@suse.cz, geert@linux-m68k.org, schmitzmic@gmail.com, rostedt@goodmis.org, mingo@redhat.com, hannes@cmpxchg.org, guro@fb.com, songmuchun@bytedance.com, weixugc@google.com, gthelen@google.com References: <20211026173822.502506-1-pasha.tatashin@soleen.com> <20211026173822.502506-4-pasha.tatashin@soleen.com> From: John Hubbard In-Reply-To: <20211026173822.502506-4-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR05CA0087.namprd05.prod.outlook.com (2603:10b6:a03:e0::28) To DM6PR12MB4140.namprd12.prod.outlook.com (2603:10b6:5:221::13) MIME-Version: 1.0 Received: from [10.2.61.40] (216.228.112.21) by BYAPR05CA0087.namprd05.prod.outlook.com (2603:10b6:a03:e0::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4649.11 via Frontend Transport; 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> + > VM_BUG_ON_PAGE(PageTail(page), page); > VM_BUG_ON_PAGE(page_ref_count(page), page); > - set_page_count(page, 1); > + refcnt = page_ref_inc_return(page); > + VM_BUG_ON_PAGE(refcnt != 1, page); Hi Pavel, I am acutely uncomfortable with this change, because it changes the meaning and behavior of the function to something completely different, while leaving the function name unchanged. Furthermore, in relies upon debug assertions, rather than a return value (for example) to verify that all is well. I understand where this patchset is going, but this intermediate step is not a good move. Also, for the overall series, if you want to change from "set_page_count()" to "inc_and_verify_val_equals_one()", then the way to do that is *not* to depend solely on VM_BUG*() to verify. Instead, return something like -EBUSY if incrementing the value results in a surprise, and let the caller decide how to handle it. thanks, -- John Hubbard NVIDIA > } > > extern unsigned long highest_memmap_pfn; >