On 15 Mar 2021, at 8:07, Kirill A. Shutemov wrote: > On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote: >> From: Zi Yan <ziy@xxxxxxxxxx> >> >> We do not have a direct user interface of splitting the compound page >> backing a THP > > But we do. You expand it. > >> and there is no need unless we want to expose the THP >> implementation details to users. Make <debugfs>/split_huge_pages accept >> a new command to do that. >> >> By writing "<pid>,<vaddr_start>,<vaddr_end>" to >> <debugfs>/split_huge_pages, THPs within the given virtual address range >> from the process with the given pid are split. It is used to test >> split_huge_page function. In addition, a selftest program is added to >> tools/testing/selftests/vm to utilize the interface by splitting >> PMD THPs and PTE-mapped THPs. >> > > Okay, makes sense. > > But it doesn't cover non-mapped THPs. tmpfs may have file backed by THP > that mapped nowhere. Do we want to cover this case too? Sure. It would be useful when large page in page cache too. I will send v4 with tmpfs THP split. I will definitely need a review for it, since I am not familiar with getting a page from a file path. > Maybe have PID:<pid>,<vaddr_start>,<vaddr_end> and > FILE:<path>,<off_start>,<off_end> ? Or just check input[0] == ‘/‘ for file path input. — Best Regards, Yan Zi
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