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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: c7g8s8myyfdmaozezt6c1mkpejhbgn7d X-Rspam-User: X-Rspamd-Queue-Id: B573F40004 X-Rspamd-Server: rspam04 X-HE-Tag: 1757907377-378555 X-HE-Meta: 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 tMgrEEKw g0eUxOe5v2bp2up9JQvfxwkYMdPmxNVPdcwtxFzrzAH1wSkxGp7R9xOM1HGb5oem5dvDFwHVk6S6YLAj4spBMHKuS38v94nGzFFeH8bsz3Rxib0sFC48rhbQ+k9/G3TUwYu1kGYI6+DIO5VA+AK2U+GMsLUl+WZnkGT5PLykI3mAAwKMWBqYQYWaD4gRUNNtkjPcLwkvc7fnTEEe/o8s86EBJiIgeBZaqAc7V8WXrTxkqPDuWPFOuBjppCJ8tgJSsi48bL4W0XOUwiZZPCi7GIeGptrOoFw9cR0Pn+NGvNYERgIZyBZKb8yqrHLLcDCHlFf2pcCzxYnHBP6orsvEbVluFUVK1PPpVfwJPaGK4v36RkK9kTOyX/gBK9P4KU72O65e22hBWLIsMF1bw/VjHekKQXQ== 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: List-Subscribe: List-Unsubscribe: On 2025/9/13 00:58, Kiryl Shutsemau wrote: > From: Kiryl Shutsemau > > MADV_COLLAPSE on a file mapping behaves inconsistently depending on if > PMD page table is installed or not. > > Consider following example: > > p = mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE, > MAP_SHARED, fd, 0); > err = madvise(p, 2UL << 20, MADV_COLLAPSE); > > fd is a populated tmpfs file. > > The result depends on the address that the kernel returns on mmap(). > If it is located in an existing PMD table, the madvise() will succeed. > However, if the table does not exist, it will fail with -EINVAL. > > This occurs because find_pmd_or_thp_or_none() returns SCAN_PMD_NULL when > a page table is missing, which causes collapse_pte_mapped_thp() to fail. > > SCAN_PMD_NULL and SCAN_PMD_NONE should be treated the same in > collapse_pte_mapped_thp(): install the PMD leaf entry and allocate page > tables as needed. > > Signed-off-by: Kiryl Shutsemau > --- Make sense to me. Thanks. Reviewed-by: Baolin Wang