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K6C6CjNAm6svEJU+Fp7NDoLmdKo5iJolGBAG44HaAQzei6pQlox45Hw9SolNmihAlA+mlUDlX8nKmhAyiDFoxGxQcmS+VUnBK9mVgCywSMMSoT0JP1RuMK1bCjfBtOijXjb190VAWgTD6xK4OG7D8/dkc0hHk0UlUa76UjTQgITZG409aZKgc319Mf+Lxag3oBSIz6xUeQxF5fTJTIlk5BPr5GqDaD9rTQMku0d5nXkPuDatQWtrN6odMjcFzndlYXbDp8q2qrqyCUoxAQWmvMv+VxyOtF1QYJliWOHe8BlxsszIQ6lcTVGcq81/3MR/7CrJcWz3A/Uu348CqrexfMXv7g1SqO/Cr8t+B2FsZP/ctZ92gbnzHcXOAYXNL6afDs6iFp6PBjW/Sqqgeva2NOD+8nd2cdgYEZcD9SBuRsJyCZ6qDZ2BIFgp+nWtEqdRm8P00PdxjPFbySRwE1BLKSNdCuA== 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 1/31/2023 4:18 AM, Vishal Moola (Oracle) wrote: > folio_estimated_sharers() takes in a folio and returns the precise > number of times the first subpage of the folio is mapped. > > This function aims to provide an estimate for the number of sharers of a > folio. This is necessary for folio conversions where we care > about the number of processes that share a folio, but don't necessarily > want to check every single page within that folio. > > This is in contrast to folio_mapcount() which calculates the total > number of the times a folio and all its subpages are mapped. > > Signed-off-by: Vishal Moola (Oracle) Reviewed-by: Yin Fengwei Regards Yin, Fengwei > --- > include/linux/mm.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 27b34f7730e7..c91bf9cdb3d0 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1905,6 +1905,24 @@ static inline size_t folio_size(struct folio *folio) > return PAGE_SIZE << folio_order(folio); > } > > +/** > + * folio_estimated_sharers - Estimate the number of sharers of a folio. > + * @folio: The folio. > + * > + * folio_estimated_sharers() aims to serve as a function to efficiently > + * estimate the number of processes sharing a folio. This is done by > + * looking at the precise mapcount of the first subpage in the folio, and > + * assuming the other subpages are the same. This may not be true for large > + * folios. If you want exact mapcounts for exact calculations, look at > + * page_mapcount() or folio_total_mapcount(). > + * > + * Return: The estimated number of processes sharing a folio. > + */ > +static inline int folio_estimated_sharers(struct folio *folio) > +{ > + return page_mapcount(folio_page(folio, 0)); > +} > + > #ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE > static inline int arch_make_page_accessible(struct page *page) > {