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vFZuJE+EsYX0dxlQL4jksTIqfyzkH5nR+ZUHWhKOft5CSOXwsKvvqP/EAGnvUlE0WDpGpmK9eRFFgJJkUHOMUylzRDZu2s69Fy0Y3uBA7qRqIeLbeDwNqgo3oPNhW7XcuRP8M0PabzjVjHxGhBO/GJLo/JVieWgErP1dEVbfpTl+RXPSdDQ4aKpqXsN6zmze+1mOFa98x/16gysQ20zq9+JjCLH79EqUscwFPpUkwiR9Ieu5MnPiRx55mr1wdydxEBJQDUxRBB1QQRbvUhTB10RCx8BmEEyW7BP5jK6WZevUfm9kzZs9n1+H+EDD2EDy24YBcQha41DTlWRxhGU1iYvPk39+eAbhrSDL5V2sbZN8Od+5wM7r2YkPBo+/lD+3SzBjTn5gKXW4/sR1gs62GpT+qNH3PpGFK5QeuTzpfDXblD9c+sX7nZMaaHgqDf4vq0yiC 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 10 Mar 2025, at 12:30, Matthew Wilcox wrote: > On Fri, Mar 07, 2025 at 12:39:55PM -0500, Zi Yan wrote: >> + for (index = new_nr_pages; index < nr_pages; index += new_nr_pages) { >> + struct page *head = &folio->page; >> + struct page *new_head = head + index; >> + >> + /* >> + * Careful: new_folio is not a "real" folio before we cleared PageTail. >> + * Don't pass it around before clear_compound_head(). >> + */ >> + struct folio *new_folio = (struct folio *)new_head; > [...] >> + /* ->mapping in first and second tail page is replaced by other uses */ >> + VM_BUG_ON_PAGE(new_nr_pages > 2 && new_head->mapping != TAIL_MAPPING, >> + new_head); >> + new_head->mapping = head->mapping; >> + new_head->index = head->index + index; > > Why are you using new_head->mapping and ->index instead of new_folio? Because of the “Careful” comment. But new_folio->* should be fine, since it is the same as new_head. So I probably can replace all new_head with new_folio except those VM_BUG_ON_PAGE checks? Best Regards, Yan, Zi