GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


man:set_mempolicy

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

NAME

     set_mempolicy  -  set  default  NUMA memory policy for a thread and its
     children

SYNOPSIS

     #include <numaif.h>
     long set_mempolicy(int mode, const unsigned long *nodemask,
                        unsigned long maxnode);
     Link with -lnuma.

DESCRIPTION

     set_mempolicy() sets the NUMA memory  policy  of  the  calling  thread,
     which  consists  of a policy mode and zero or more nodes, to the values
     specified by the mode, nodemask and maxnode arguments.
     A NUMA machine has different memory  controllers  with  different  dis-
     tances  to  specific  CPUs.   The memory policy defines from which node
     memory is allocated for the thread.
     This system call defines the default policy for the thread.  The thread
     policy  governs allocation of pages in the process's address space out-
     side of memory ranges controlled by  a  more  specific  policy  set  by
     mbind(2).   The  thread  default policy also controls allocation of any
     pages for memory-mapped files mapped using the mmap(2)  call  with  the
     MAP_PRIVATE flag and that are only read (loaded) from by the thread and
     of  memory-mapped  files  mapped  using  the  mmap(2)  call  with   the
     MAP_SHARED  flag, regardless of the access type.  The policy is applied
     only when a new page is allocated for the thread.  For anonymous memory
     this is when the page is first touched by the thread.
     The   mode  argument  must  specify  one  of  MPOL_DEFAULT,  MPOL_BIND,
     MPOL_INTERLEAVE, MPOL_PREFERRED, or MPOL_LOCAL (which are described  in
     detail  below).   All  modes  except MPOL_DEFAULT require the caller to
     specify the node or nodes to which the mode applies, via  the  nodemask
     argument.
     The  mode  argument  may  also include an optional mode flag.  The sup-
     ported mode flags are:
     MPOL_F_STATIC_NODES (since Linux 2.6.26)
            A nonempty nodemask specifies physical node IDs.  Linux will not
            remap  the nodemask when the process moves to a different cpuset
            context, nor when the set of nodes allowed by the process's cur-
            rent cpuset context changes.
     MPOL_F_RELATIVE_NODES (since Linux 2.6.26)
            A  nonempty nodemask specifies node IDs that are relative to the
            set of node IDs allowed by the process's current cpuset.
     nodemask points to a bit mask of node IDs that contains up  to  maxnode
     bits.    The  bit  mask  size  is  rounded  to  the  next  multiple  of
     sizeof(unsigned long), but the kernel will use bits only 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.
     Where a nodemask is required, it must contain at least one node that is
     on-line, allowed by the process's current cpuset context,  (unless  the
     MPOL_F_STATIC_NODES  mode  flag is specified), and contains memory.  If
     the MPOL_F_STATIC_NODES is set in mode and a required nodemask contains
     no  nodes that are allowed by the process's current cpuset context, the
     memory policy reverts to local allocation.  This effectively  overrides
     the specified policy until the process's cpuset context includes one or
     more of the nodes specified by nodemask.
     The mode argument must include one of the following values:
     MPOL_DEFAULT
            This mode specifies that any nondefault thread memory policy  be
            removed,  so  that  the memory policy "falls back" to the system
            default policy.  The system default  policy  is  "local  alloca-
            tion"--that  is,  allocate  memory  on  the node of the CPU that
            triggered the allocation.  nodemask must be specified  as  NULL.
            If  the  "local  node"  contains no free memory, the system will
            attempt to allocate memory from a "near by" node.
     MPOL_BIND
            This mode defines a strict policy that restricts memory  alloca-
            tion  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 node-
            mask.
     MPOL_INTERLEAVE
            This mode interleaves page allocations across the  nodes  speci-
            fied  in  nodemask in numeric node ID order.  This optimizes for
            bandwidth instead of latency by spreading out pages  and  memory
            accesses   to  those  pages  across  multiple  nodes.   However,
            accesses to a single page will still be limited  to  the  memory
            bandwidth of a single node.
     MPOL_PREFERRED
            This  mode  sets  the preferred node for allocation.  The kernel
            will try to allocate pages from this node first and fall back to
            "near by" nodes if the preferred node 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  policy
            specifies  "local  allocation"  (like  the system default policy
            discussed above).
     MPOL_LOCAL (since Linux 3.8)
            This mode specifies "local allocation"; the memory is  allocated
            on the node of the CPU that triggered the allocation (the "local
            node").  The nodemask and maxnode  arguments  must  specify  the
            empty  set.  If the "local node" is low on free memory, the ker-
            nel will try to allocate memory from other  nodes.   The  kernel
            will  allocate  memory from the "local node" whenever memory for
            this node is available.  If the "local node" is not  allowed  by
            the  process's  current  cpuset  context, the kernel will try to
            allocate memory from other nodes.  The kernel will allocate mem-
            ory  from  the  "local  node" whenever it becomes allowed by the
            process's current cpuset context.
     The thread memory policy is  preserved  across  an  execve(2),  and  is
     inherited by child threads created using fork(2) or clone(2).

RETURN VALUE

     On  success,  set_mempolicy()  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.
     EINVAL mode  is  invalid.   Or,  mode  is  MPOL_DEFAULT and nodemask is
            nonempty, or mode is MPOL_BIND or MPOL_INTERLEAVE  and  nodemask
            is empty.  Or, maxnode specifies more than a page worth of bits.
            Or, nodemask specifies one or more node  IDs  that  are  greater
            than  the  maximum  supported node ID.  Or, none of the node IDs
            specified by nodemask are on-line and allowed by  the  process's
            current  cpuset  context, or none of the specified nodes contain
            memory.     Or,    the    mode    argument    specified     both
            MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES.
     ENOMEM Insufficient kernel memory was available.

VERSIONS

     The  set_mempolicy()  system call was added to the Linux kernel in ver-
     sion 2.6.7.

CONFORMING TO

     This system call is Linux-specific.

NOTES

     Memory policy is not remembered if the page is swapped out.  When  such
     a page is paged back in, it will use the policy of the thread or memory
     range that is in effect at the time the page is allocated.
     For information on library support, see numa(7).

SEE ALSO

     get_mempolicy(2), getcpu(2),  mbind(2),  mmap(2),  numa(3),  cpuset(7),
     numa(7), numactl(8)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 SET_MEMPOLICY(2)

/data/webs/external/dokuwiki/data/pages/man/set_mempolicy.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki