UFFDIO_MOVE(2const) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON

UFFDIO_MOVE(2const)                                   UFFDIO_MOVE(2const)

NAME         top

       UFFDIO_MOVE - atomically move a continuous memory chunk into the
       userfault registered range

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <linux/userfaultfd.h>  /* Definition of UFFD* constants */
       #include <sys/ioctl.h>

       int ioctl(int fd, UFFDIO_MOVE, struct uffdio_move *argp);

       #include <linux/userfaultfd.h>

       struct uffdio_move {
           __u64  dst;   /* Destination of move */
           __u64  src;   /* Source of move */
           __u64  len;   /* Number of bytes to move */
           __u64  mode;  /* Flags controlling behavior of move */
           __s64  move;  /* Number of bytes moved, or negated error */
       };

DESCRIPTION         top

       Atomically move a continuous memory chunk into the userfault
       registered range and optionally wake up the blocked thread.

       The following value may be bitwise ORed in .mode to change the
       behavior of the UFFDIO_MOVE operation:

       UFFDIO_MOVE_MODE_DONTWAKE
              Do not wake up the thread that waits for page-fault
              resolution

       UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES
              Allow holes in the source virtual range that is being
              moved.  When not specified, the holes will result in ENOENT
              error.  When specified, the holes will be accounted as
              successfully moved memory.  This is mostly useful to move
              hugepage aligned virtual regions without knowing if there
              are transparent hugepages in the regions or not, but
              preventing the risk of having to split the hugepage during
              the operation.

       The .move field is used by the kernel to return the number of
       bytes that was actually moved, or an error (a negated errno-style
       value).  The .move field is output-only; it is not read by the
       UFFDIO_MOVE operation.

RETURN VALUE         top

       On success, 0 is returned.  In this case, the entire area was
       moved.

       On error, -1 is returned and errno is set to indicate the error.

ERRORS         top

       EAGAIN The number of bytes moved (i.e., the value returned in the
              .move field) does not equal the value that was specified in
              the .len field.

       EINVAL Either .dst or .len was not a multiple of the system page
              size, or the range specified by .src and .len or .dst and
              .len was invalid.

       EINVAL An invalid bit was specified in the .mode field.

       ENOENT The source virtual memory range has unmapped holes and
              UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set.

       EEXIST The destination virtual memory range is fully or partially
              mapped.

       EBUSY  The pages in the source virtual memory range are either
              pinned or not exclusive to the process.  Once KSM
              deduplicates pages or fork(2) COW-shares pages during
              fork(2) with child processes, they are no longer exclusive.
              The kernel might only perform lightweight checks for
              detecting whether the pages are exclusive.  To make the
              operation more likely to succeed, KSM should be disabled,
              fork(2) should be avoided or MADV_DONTFORK should be
              configured for the source virtual memory area before
              fork(2).

       ENOMEM Allocating memory needed for the operation failed.

       ESRCH  The target process has exited at the time of a UFFDIO_MOVE
              operation.

STANDARDS         top

       Linux.

HISTORY         top

       Linux 6.8.

SEE ALSO         top

       ioctl(2), ioctl_userfaultfd(2), userfaultfd(2)

       linux.git/Documentation/admin-guide/mm/userfaultfd.rst

COLOPHON         top

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Linux man-pages 6.15            2025-05-17            UFFDIO_MOVE(2const)

Pages that refer to this page: ioctl_userfaultfd(2)