MBIND(2) | Linux Programmer's Manual | MBIND(2) |
mbind - set memory policy for a memory range
#include <numaif.h>
long mbind(void *addr, unsigned long len, int mode, const unsigned long *nodemask, unsigned long maxnode, unsigned flags);
Link with -lnuma.
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 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 be allocated only 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 memory policy of the thread that causes the page to be allocated. This may not be the thread 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 memory policy of the thread that caused the page to be allocated. Again, this may not be the thread 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 of which process attached to the shared memory segment causes the allocation. If, however, 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 process that calls mbind() for that region.
By default, mbind() has an effect only 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, MPOL_PREFERRED, or MPOL_LOCAL (which are described in detail below). All policy 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 supported mode flags are:
nodemask points to a bit mask 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 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 thread's current cpuset context (unless the MPOL_F_STATIC_NODES mode flag is specified), and contains memory.
The mode argument must include one of the following values:
If MPOL_MF_STRICT is passed in flags and mode is not MPOL_DEFAULT, then the call fails 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 fails 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 thread must be privileged (CAP_SYS_NICE) to use this flag. If MPOL_MF_STRICT is also specified, then the call fails with the error EIO if some pages could not be moved.
On success, mbind() returns 0; on error, -1 is returned and errno is set to indicate the error.
The mbind() system call was added to the Linux kernel in version 2.6.7.
This system call is Linux-specific.
For information on library support, see numa(7).
NUMA policy is not supported on a memory-mapped file range that was mapped with the MAP_SHARED flag.
The MPOL_DEFAULT mode can have different effects for mbind() and set_mempolicy(2). When MPOL_DEFAULT is specified for set_mempolicy(2), the thread's memory policy reverts to the system default policy or local allocation. When MPOL_DEFAULT is specified for a range of memory using mbind(), any pages subsequently allocated for that range will use the thread's memory policy, as set by set_mempolicy(2). This effectively removes the explicit policy from the specified range, "falling back" to a possibly nondefault policy. To select explicit "local allocation" for a memory range, specify a mode of MPOL_LOCAL or MPOL_PREFERRED with an empty set of nodes. This method will work for set_mempolicy(2), as well.
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_STRICT is ignored on huge page mappings.
MPOL_MF_MOVE and MPOL_MF_MOVE_ALL are available only on Linux 2.6.16 and later.
get_mempolicy(2), getcpu(2), mmap(2), set_mempolicy(2), shmat(2), shmget(2), numa(3), cpuset(7), numa(7), numactl(8)
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/.
2017-09-15 | Linux |