On Mon, Dec 23, 2019 at 08:16:53PM +0300, Kirill A. Shutemov wrote: >On Mon, Dec 23, 2019 at 10:24:35AM +0800, Wei Yang wrote: >> There are two cases to call try_to_unmap_one() with TTU_SPLIT_HUGE_PMD >> set: >> >> * unmap_page() >> * shrink_page_list() >> >> In both case, the page passed to try_to_unmap_one() is PageHead() of the >> THP. If this page's mapping address in process is not HPAGE_PMD_SIZE >> aligned, this means the THP is not mapped as PMD THP in this process. >> This could happen when we do mremap() a PMD size range to an un-aligned >> address. >> >> Currently, this case is handled by following check in __split_huge_pmd() >> luckily. >> >> page != pmd_page(*pmd) >> >> This patch checks the address to skip some hard work. > >Do you see some measurable performance improvement? rmap is heavy enough >and I expect this kind of overhead to be within noise level. > >I don't have anything agains the check, but it complicates the picture. > >And if we are going this path, it worth also check if the vma is long >enough to hold huge page. > >And I don't see why the check cannot be done inside split_huge_pmd_address(). > Ok, let me put the check into split_huge_pmd_address(). >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me
