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MBIND(2)                   Linux Programmer's Manual                  MBIND(2)



NAME
       mbind - Set memory policy for a memory range

SYNOPSIS
       #include <&lt;numaif.h>&gt;

       int mbind(void *addr, unsigned long len, int mode,
                 unsigned long *nodemask, unsigned long maxnode,
                 unsigned flags);

       Link with -lnuma

DESCRIPTION
       mbind()  sets  the  NUMA memory policy, which consists of a policy mode
       and zero or more nodes, for the memory range  starting  with  addr  and
       continuing for len bytes.  The memory of a NUMA machine is divided into
       multiple nodes.  The memory policy defines from which  node  memory  is
       allocated.

       If the memory range specified by the addr and len arguments includes an
       "anonymous" region of memory--that is a region of memory created  using
       the  mmap(2)  system  call  with  the MAP_ANONYMOUS--or a memory mapped
       file, mapped using the mmap(2) system call with the  MAP_PRIVATE  flag,
       pages will only be allocated according to the specified policy when the
       application writes [stores] to the page.   For  anonymous  regions,  an
       initial read access will use a shared page in the kernel containing all
       zeros.  For a file mapped with MAP_PRIVATE, an initial read access will
       allocate  pages  according  to  the  process policy of the process that
       causes the page to be allocated.  This may  not  be  the  process  that
       called mbind().

       The specified policy will be ignored for any MAP_SHARED mappings in the
       specified memory range.  Rather the pages will be  allocated  according
       to  the  process policy of the process that caused the page to be allo-
       cated.  Again, this may not be the process that called mbind().

       If the specified memory range includes a shared memory  region  created
       using  the shmget(2) system call and attached using the shmat(2) system
       call, pages allocated for the anonymous or shared memory region will be
       allocated  according  to the policy specified, regardless which process
       attached to the shared memory segment causes the allocation.  If,  how-
       ever,  the  shared memory region was created with the SHM_HUGETLB flag,
       the huge pages will be allocated according to the policy specified only
       if  the  page  allocation  is caused by the task that calls mbind() for
       that region.

       By default, mbind() only has an effect  for  new  allocations;  if  the
       pages  inside  the  range  have been already touched before setting the
       policy, then the policy has no effect.  This default  behavior  may  be
       overridden  by  the  MPOL_MF_MOVE  and MPOL_MF_MOVE_ALL flags described
       below.

       The  mode  argument  must  specify  one  of  MPOL_DEFAULT,   MPOL_BIND,
       MPOL_INTERLEAVE   or   MPOL_PREFERRED.    All   policy   modes   except
       MPOL_DEFAULT require the caller to specify via the  nodemask  argument,
       the node or nodes to which the mode applies.

       nodemask  points  to  a bitmask of nodes containing up to maxnode bits.
       The bit mask size is rounded to the next  multiple  of  sizeof(unsigned
       long),  but  the kernel will only use bits up to maxnode.  A NULL value
       of nodemask or a maxnode value of  zero  specifies  the  empty  set  of
       nodes.   If  the  value  of  maxnode  is zero, the nodemask argument is
       ignored.

       The MPOL_DEFAULT mode specifies that the default policy should be used.
       When  applied  to  a range of memory via mbind(), this means to use the
       process policy, which may have been set with set_mempolicy(2).  If  the
       mode  of  the  process  policy  is  also  MPOL_DEFAULT, the system-wide
       default policy will be used.  The system-wide default policy will allo-
       cate  pages  on  the node of the CPU that triggers the allocation.  For
       MPOL_DEFAULT, the nodemask and maxnode arguments must  be  specify  the
       empty set of nodes.

       The  MPOL_BIND  mode  specifies  a  strict policy that restricts memory
       allocation to the nodes specified in nodemask.  If  nodemask  specifies
       more  than  one node, page allocations will come from the node with the
       lowest numeric node ID first, until that node contains no free  memory.
       Allocations  will then come from the node with the next highest node ID
       specified in nodemask and so forth, until none of the  specified  nodes
       contain  free  memory.   Pages  will not be allocated from any node not
       specified in the nodemask.

       The MPOL_INTERLEAVE mode specifies that page allocations be interleaved
       across  the  set  of  nodes  specified in nodemask.  This optimizes for
       bandwidth instead of latency by spreading out pages and memory accesses
       to  those pages across multiple nodes.  To be effective the memory area
       should be fairly large, at least 1MB or bigger with  a  fairly  uniform
       access  pattern.   Accesses  to a single page of the area will still be
       limited to the memory bandwidth of a single node.

       MPOL_PREFERRED sets the preferred node for allocation.  The kernel will
       try to allocate pages from this node first and fall back to other nodes
       if the preferred nodes is low on free memory.   If  nodemask  specifies
       more  than  one node ID, the first node in the mask will be selected as
       the preferred node.  If the nodemask and maxnode arguments specify  the
       empty  set,  then  the  memory is allocated on the node of the CPU that
       triggered the allocation.  This is the only way to specify "local allo-
       cation" for a range of memory via mbind().

       If  MPOL_MF_STRICT  is  passed in flags and policy is not MPOL_DEFAULT,
       then the call will fail with the error EIO if the existing pages in the
       memory range don't follow the policy.

       If  MPOL_MF_MOVE is specified in flags, then the kernel will attempt to
       move all the existing pages in the memory range so that they follow the
       policy.   Pages that are shared with other processes will not be moved.
       If MPOL_MF_STRICT is also specified, then the call will fail  with  the
       error EIO if some pages could not be moved.

       If MPOL_MF_MOVE_ALL is passed in flags, then the kernel will attempt to
       move all existing pages in the memory range regardless of whether other
       processes  use  the  pages.   The  calling  process  must be privileged
       (CAP_SYS_NICE) to use this flag.  If MPOL_MF_STRICT is also  specified,
       then  the  call will fail with the error EIO if some pages could not be
       moved.

RETURN VALUE
       On success, mbind() returns 0; on error, -1 is returned  and  errno  is
       set to indicate the error.

ERRORS
       EFAULT Part  of all of the memory range specified by nodemask and maxn-
              ode points outside your accessible address space.  Or, there was
              an unmapped hole in the specified memory range.

       EINVAL An  invalid value was specified for flags or mode; or addr + len
              was less than addr; or addr is not a multiple of the system page
              size.   Or,  mode  is MPOL_DEFAULT and nodemask specified a non-
              empty set; or mode is MPOL_BIND or MPOL_INTERLEAVE and  nodemask
              is  empty.  Or, maxnode exceeds kernel-imposed limit.  Or, node-
              mask specifies one or more node IDs that are  greater  than  the
              maximum  supported  node  ID,  or are not allowed in the calling
              task's context.  Or, none of the node IDs specified by  nodemask
              are on-line, or none of the specified nodes contain memory.

       EIO    MPOL_MF_STRICT was specified and an existing page was already on
              a node that does not  follow  the  policy;  or  MPOL_MF_MOVE  or
              MPOL_MF_MOVE_ALL was specified and the kernel was unable to move
              all existing pages in the range.

       ENOMEM Insufficient kernel memory was available.

       EPERM  The flags argument included the MPOL_MF_MOVE_ALL  flag  and  the
              caller does not have the CAP_SYS_NICE privilege.

CONFORMING TO
       This system call is Linux-specific.

NOTES
       NUMA  policy  is  not  supported on a memory mapped file range that was
       mapped with the MAP_SHARED flag.

       MPOL_MF_STRICT is ignored on huge page mappings.

       The MPOL_DEFAULT, mode has different effects for mbind()  and  set_mem-
       policy(2).   When MPOL_DEFAULT is specified for a range of memory using
       mbind(), any pages subsequently allocated for that range will  use  the
       process's policy, as set by set_mempolicy(2).  This effectively removes
       the explicit policy from the specified range.  To select "local alloca-
       tion"  for  a  memory  range,  specify a mode of MPOL_PREFERRED with an
       empty set of nodes.  This method will  work  for  set_mempolicy(2),  as
       well.

   Versions and Library Support
       The  mbind(),  get_mempolicy(2), and set_mempolicy(2) system calls were
       added to the Linux kernel with version 2.6.7.  They are only  available
       on kernels compiled with CONFIG_NUMA.

       You  can  link with -lnuma to get system call definitions.  libnuma and
       the required &lt;numaif.h&gt; header are available in the numactl package.

       However, applications should  not  use  these  system  calls  directly.
       Instead,  the  higher level interface provided by the numa(3) functions
       in the numactl package is recommended.  The numactl package  is  avail-
       able at http://oss.sgi.com/www/projects/libnuma/download/.  The package
       is also included  in  some  Linux  distributions.   Some  distributions
       include  the  development  library  and header in the separate numactl-
       devel package.

       Support for huge page policy was added  with  2.6.16.   For  interleave
       policy  to be effective on huge page mappings the policied memory needs
       to be tens of megabytes or larger.

       MPOL_MF_MOVE and MPOL_MF_MOVE_ALL are only available  on  Linux  2.6.16
       and later.

SEE ALSO
       get_mempolicy(2),   getcpu(2),   mmap(2),  set_mempolicy(2),  shmat(2),
       shmget(2), numa(3), cpuset(7), numactl(8)

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-05-22                          MBIND(2)