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cachestat(2) — Linux manual page

cachestat(2)               System Calls Manualcachestat(2)

NAME        top

       cachestat - query the page cache statistics of a file

SYNOPSIS        top

#include <sys/mman.h>int cachestat(unsigned intfd, struct cachestat_range *cstat_range,struct cachestat *cstat, unsigned intflags);struct cachestat_range {__u64 off;__u64 len;};struct cachestat {__u64 nr_cache;__u64 nr_dirty;__u64 nr_writeback;__u64 nr_evicted;__u64 nr_recently_evicted;};

DESCRIPTION        top

cachestat()queries the number of cached pages, dirty pages, pages       marked for writeback, evicted pages, and recently evicted pages in       the byte range specified by.off and.len in thecachestat_range       structure.       An evicted page is one that was previously in the page cache but       has since been evicted.  A page is considered recently evicted if       its reentry into the cache would indicate active usage under       memory pressure.       The results are returned in acachestatstructure, pointed to by       thecstat argument.       The.off and.len fields must be non-negative.  If.len > 0, the       queried range is [.off,.off+.len].  Iflen == 0, the range is       from.off to the end of the file.       Theflags argument is reserved for future use and must be set to0.       Currently,hugetlbfsfiles are not supported.

RETURN VALUE        top

       On success,cachestat()returns 0.  On error, -1 is returned, anderrno is set to indicate the error.

ERRORS        top

EFAULTcstat orcstat_range point to an invalid address.EINVALInvalidflags value.EBADFInvalid file descriptor.EOPNOTSUPP              The file descriptor refers to ahugetlbfsfile, which is              unsupported.

STANDARDS        top

       Linux.

HISTORY        top

       Linux 6.5.

CAVEATS        top

       Note that the status of a page may change aftercachestat()       retrieves it but before the values are returned to the       application; thus, the values may be slightly outdated.

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-06-28cachestat(2)

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