get_mempolicy(2)
SECCIĆN: 2 - Llamadas al sistema
get_mempolicy(2) System Calls Manual get_mempolicy(2)
NAME
get_mempolicy - retrieve NUMA memory policy for a thread
LIBRARY
NUMA (Non-Uniform Memory Access) policy library (libnuma, -lnuma)
SYNOPSIS
#include <numaif.h>
long get_mempolicy(int *mode,
unsigned long nodemask[(.maxnode + ULONG_WIDTH - 1)
/ ULONG_WIDTH],
unsigned long maxnode, void *addr,
unsigned long flags);
DESCRIPTION
get_mempolicy() retrieves the NUMA policy of the calling thread or of a
memory address, depending on the setting of flags.
A NUMA machine has different memory controllers with different disā
tances to specific CPUs. The memory policy defines from which node
memory is allocated for the thread.
If flags is specified as 0, then information about the calling thread's
default policy (as set by set_mempolicy(2)) is returned, in the buffers
pointed to by mode and nodemask. The value returned in these arguments
may be used to restore the thread's policy to its state at the time of
the call to get_mempolicy() using set_mempolicy(2). When flags is 0,
addr must be specified as NULL.
If flags specifies MPOL_F_MEMS_ALLOWED (available since Linux 2.6.24),
the mode argument is ignored and the set of nodes (memories) that the
thread is allowed to specify in subsequent calls to mbind(2) or
set_mempolicy(2) (in the absence of any mode flags) is returned in
nodemask. It is not permitted to combine MPOL_F_MEMS_ALLOWED with eiā
ther MPOL_F_ADDR or MPOL_F_NODE.
If flags specifies MPOL_F_ADDR, then information is returned about the
policy governing the memory address given in addr. This policy may be
different from the thread's default policy if mbind(2) or one of the
helper functions described in numa(3) has been used to establish a polā
icy for the memory range containing addr.
If the mode argument is not NULL, then get_mempolicy() will store the
policy mode and any optional mode flags of the requested NUMA policy in
the location pointed to by this argument. If nodemask is not NULL,
then the nodemask associated with the policy will be stored in the loā
cation pointed to by this argument. maxnode specifies the number of
node IDs that can be stored into nodemaskāthat is, the maximum node ID
plus one. The value specified by maxnode is always rounded to a multiā
ple of sizeof(unsigned long)*8.
If flags specifies both MPOL_F_NODE and MPOL_F_ADDR, get_mempolicy()
will return the node ID of the node on which the address addr is alloā
cated into the location pointed to by mode. If no page has yet been
allocated for the specified address, get_mempolicy() will allocate a
page as if the thread had performed a read (load) access to that adā
dress, and return the ID of the node where that page was allocated.
If flags specifies MPOL_F_NODE, but not MPOL_F_ADDR, and the thread's
current policy is MPOL_INTERLEAVE, then get_mempolicy() will return in
the location pointed to by a non-NULL mode argument, the node ID of the
next node that will be used for interleaving of internal kernel pages
allocated on behalf of the thread. These allocations include pages for
memory-mapped files in process memory ranges mapped using the mmap(2)
call with the MAP_PRIVATE flag for read accesses, and in memory ranges
mapped with the MAP_SHARED flag for all accesses.
Other flag values are reserved.
For an overview of the possible policies see set_mempolicy(2).
RETURN VALUE
On success, get_mempolicy() returns 0; on error, -1 is returned and erā
rno is set to indicate the error.
ERRORS
EFAULT Part of all of the memory range specified by nodemask and maxnā
ode points outside your accessible address space.
EINVAL The value specified by maxnode is less than the number of node
IDs supported by the system. Or flags specified values other
than MPOL_F_NODE or MPOL_F_ADDR; or flags specified MPOL_F_ADDR
and addr is NULL, or flags did not specify MPOL_F_ADDR and addr
is not NULL. Or, flags specified MPOL_F_NODE but not
MPOL_F_ADDR and the current thread policy is not MPOL_INTERā
LEAVE. Or, flags specified MPOL_F_MEMS_ALLOWED with either
MPOL_F_ADDR or MPOL_F_NODE. (And there are other EINVAL cases.)
VERSIONS
The get_mempolicy() system call was added in Linux 2.6.7.
STANDARDS
This system call is Linux-specific.
NOTES
For information on library support, see numa(7).
SEE ALSO
getcpu(2), mbind(2), mmap(2), set_mempolicy(2), numa(3), numa(7), nuā
mactl(8)
Linux man-pages 6.03 2023-02-05 get_mempolicy(2)
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