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Shutemov" , Yang Shi , David Hildenbrand , Hugh Dickins , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/khugepaged: set THP as uptodate earlier for shmem Message-ID: References: <20230214075710.2401855-1-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230214075710.2401855-1-stevensd@google.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 15F9880017 X-Stat-Signature: 1fy418u84o5i84ytcs8yhi3br1nfdx6q X-HE-Tag: 1676389500-232295 X-HE-Meta: U2FsdGVkX18QFaV8EZrOl/+MMygwy6008CVK4/vckP3+arLI/FeW8GXfdvPk9yN3ZptB94/LrZNglOw6h11SKNC8ImiDst/DegwzxvLtkL3pP6cNPqVorSkWcMnKoFBNcBr2keUMxHX3CcEWtbut2tk+VcNLfpegjy5vSEui4n5hvzqs8OEwi4LPJLblIZkfSsSj1tZygx54wUj7XjFUeQpc9ptF3C3e+VMIvOtqz1TrdfXXyMcyVOJlsqM5UDsp7RYSghQfpIh9p7R940XNcoKLIkkIBC+iWntbi9dENwin1D5o5iTsyqBy1Hs9VK079+txh2+RFp/PWPaeOYySuNch7XgSmcfaFByf9qHBCEnYPajsTeFSM4t8r+S+Uhu1cnB/A9vi9FMe5ajaF+FDLDvodEeFk5FIWybUGIwTJkRfQQ2PcqySEkBr0UQI5WBTTprKFDSn8V8npcwB50nlhFTmNqbMe14LNRhuuetEfzpgtR+xVPP6atbZUAftYR+As/j3H1g1tZFATAfg6OrIGPDUeWIJIMlEqANTk6WT8xm64Yojs9Eepn6D+JoJqHVapBy8XpKAQCr3x5L/A2KnXRu1qIgL/K1q+49eqGD3YbzUKSlLid2OC/6++SmvyPXTFMwhAsjPu6HrG8aafTJ/ivHPa90ZKPFt3oMcfuIWz+F3d8rwQrX4v9tOEiQppkRsZICBysWt/26JhvprRZrNOZkkpJx6cCp6VbmmiWu0RgjEjzxCgdup0ejcVJsoOiaMEjcpXk2lOCShFBfr4K9hVBJyf5F+cwwdNtgmIDTcnWLKkqJ/KHnwl6PTvsnH3mCvNcSD50pskjnUFCa6blMvBqCEFeOAC6AtlssQjtQoFR/Gddo68xvrXomy8nO1oqTLdjmAGz42RPtNUHccHu+PDWXprXELe9vhypOz2ndnLVUgCyvburwHQKrtnQ1v+fe8FFWr0FjGdi3xvtHHE0r Neax59HK +Lu3l0Bl7mPrIrcaPa4DFi36tv6orjNHLbklv8DC2lq1NHCXb7tGa74JzexNpmAmBXnBKfhyAM0qAe/K+D1wOLFe1VyNsKNSh2iyGcIg15pGhexbKzaYowtR2PoPo7X8zbku6GkXx4h0AJgWGkoEA5WmRlg== 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 Tue, Feb 14, 2023 at 04:57:09PM +0900, David Stevens wrote: > /* > - * At this point the hpage is locked and not up-to-date. > - * It's safe to insert it into the page cache, because nobody would > - * be able to map it or use it in another way until we unlock it. > + * Mark hpage as up-to-date before inserting it into the page cache to > + * prevent it from being mistaken for an fallocated but unwritten page. > + * Inserting the unfinished hpage into the page cache is safe because > + * it is locked, so nobody can map it or use it in another way until we > + * unlock it. No, that's not true. The data has to be there before we mark it uptodate. See filemap_get_pages() for example, used as part of read(). We don't lock the page unless we need to bring it uptodate ourselves.