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nfork(3)
NAME
nfork - Creates a child process (libnuma library)
SYNOPSIS
#include <numa.h>
pid_t nfork(
numa_attr_t *numa_attr );
PARAMETERS
numa_attr
Points to a structure of type numa_attr_t that contains the following
members:
nattr_type
The type of resource to which the child process will be
attached, or near which the child process will be located.
nattr_descr
The resource descriptor for the resource to which the child
process will be attached, or near which the child process will
be located.
nattr_distance
The distance criteria for selecting resources. RADs in the
caller's partition that have a distance (from the specified
resource) equal to or less than this value will be considered
as candidates for the child process's location.
nattr_flags
A bit mask of options that help control how the system assigns
a "home RAD" to the child process.
The following symbolic values are defined for this bit mask:
RAD_INSIST
The requested RAD assignment is mandatory. The child
process will be created on one of the RADs in the
specified RAD set regardless of the CPU or memory load
of the specified RADs.
RAD_NO_INHERIT
The child process might not be assigned to the same
home RAD as its parent process. Allows the system to
assign a home RAD to the child process depending on
available resources.
Normally, child processes do inherit the assignments
and attributes of the parent process.
RAD_SMALLMEM
The process has "small memory" requirements, so the
system should favor (for the child process's home RAD)
those RADs with light CPU loads, independent of their
available memory.
RAD_LARGEMEM
The process has large memory requirements, so the
system should favor (for the child process's home RAD)
those RADs with more available memory, independent of
CPU loads.
If numa_attr is NULL, the function behaves as fork().
DESCRIPTION
The nfork() function causes creation of a new process. The new process
(child process) is an exact copy of the calling process (parent process).
This means the child process inherits the following attributes from the
parent process:
· Environment
· Close-on-exec flag. See exec(2).
· Signal-handling settings (in other words, SIG_DFL, SIG_IGN, SIG_HOLD,
function address)
· Set-user-ID mode bit
· Set-group-ID mode bit
· Trusted state
· Profiling on/off status
· Nice value. See nice(2).
· All attached shared libraries
· Process group ID
· Session ID (tty group ID)
· Foreground process ID. See exit(2).
· Current working directory
· Root directory
· File mode creation mask. See umask(2).
· File size limit. See ulimit(2).
· All attached shared memory segments. See shmat(2).
· All attached mapped regions. See mmap(2) and nmmap(3).
· All mapped regions with the same protection and sharing mode as in the
parent process.
The child process differs from the parent process in the following ways:
· The child process has a unique process ID that does not match any
active process group ID.
· The parent process ID of the child process matches the process ID of
the parent.
· The child process has its own copy of the parent process's file
descriptors. Each of the child's file descriptors refers to the same
open file description with the corresponding file descriptor of the
parent process.
· The child process has its own copy of the parent's open directory
streams. Each open directory stream in the child process may share
directory stream positioning with the corresponding directory stream
of the parent.
· All semadj values are cleared.
· Process locks, text locks and data locks are not inherited by the
child. See plock(2).
· The child process's values of tms_utime, tms_stime, tms_cutime, and
tms_cstime are set to 0.
· Any pending alarms are cleared in the child process.
· Any interval timers enabled by the parent process are reset in the
child process.
· Any signals pending for the parent process are cleared for the child
process.
· The NUMA scheduling parameters and memory allocation attributes of the
child process may be different from those of the parent process.
The nfork() function is used when the caller wishes to specify the location
where the child process should be loaded. If the nattr_descr field is NULL,
the nfork() function behaves identically to the fork() function, and the
child process inherits the calling thread's memory allocation policy and
attributes. However, the nattr_flags field may still affect how the system
selects a home RAD for the child process, as described in PARAMETERS.
If the nattr_descr field is non-NULL, it, along with the nattr_type and
nattr_distance fields, identifies the acceptable RADs from which to select
the child process's home RAD. The memory allocation policy for the child
process will be set to MPOL_THREAD.
If nattr_type is anything other than R_RAD or R_NSG, nfork() will behave as
though nloc() were called to obtain a RAD set that meets the specified
criteria, and then nfork() were called with nattr_type equal to R_RAD, and
nattr_descr pointing to the RAD set returned by nloc(). This behavior is
described below. The nattr_distance parameter is ignored for a nattr_type
of R_RAD or R_NSG.
If the nattr_descr field is equal to R_RAD, then nattr_descr points to a
radset_t that identifies the acceptable RADs from which to select the child
process's initial home RAD. The remainder of the RAD set (in other words,
the set less the child process's home RAD) becomes the child's overflow
set.
A suitable set of RADs can be located according to available resources by
nloc() and can be manipulated using the operators described for
radsetops(). Unless RAD_INSIST has been set in nattr_flags, the specified
RAD set is considered a hint, which may be overridden if all the RADs in
the specified set have very high CPU loads or too little available memory.
If the RAD_INSIST flag is specified in nattr_flags, the RAD specification
is treated as mandatory, and the child process is assigned to one of the
specified RADs despite a large CPU load or memory shortage.
When using nfork(), the caller can further specify an appropriate RAD by
setting the RAD_SMALLMEM or RAD_LARGEMEM bits in the nattr_flags field.
RAD_SMALLMEM indicates that the child will have very low memory
requirements, so can be placed on a RAD having little available memory if
that RAD has a particularly light CPU load. Conversely, if RAD_LARGEMEM is
set, the process is placed on the RAD with the most available memory even
though that RAD may have a high CPU load. RAD_SMALLMEM and RAD_LARGEMEM
are also taken into account during any future process migrations.
If the nattr_descr field is equal to R_NSG, then nattr_descr specifies a
NUMA Scheduling Group (NSG) as returned by nsg_init(). The child process
will be attached to the NSG and will receive the same home RAD as the other
members in the NSG. If the child process is the first process to attach to
the NSG, then the home RAD for the child will be inherited from the calling
thread, just as for the fork() function.
NOTES
The nfork() function is supported for multithreaded applications.
If a multithreaded process calls the nfork() function, the new process
contains a replica of the calling thread and its entire address space,
possibly including the states of mutexes and other resources. Consequently,
to avoid errors, the child process should only execute operations that will
not cause deadlock until one of the exec functions is called.
The set of valid resources that may be specified is constrained by the
caller's partition.
RETURN VALUES
0 Success (returned to the child process). In this case, the function
also returns the process ID of the child process to the parent process.
The child process and all of the related data structures will be
allocated on one of the RADs selected by the system scheduler from
among those specified by the nattr_type, nattr_descr, and
nattr_distance fields. The initial thread of the child process will be
scheduled on one of the available CPUs in the selected RAD.
-1 Failure (returned to the parent process). In this case, no child
process is created, and errno is set to indicate the error.
ERRORS
If the nfork() function fails, it sets errno to one of the following values
for the condition specified:
[EAGAIN]
The limit on the total number of processes executing for a single user
would be exceeded. This limit can be exceeded by a process with
superuser privilege.
[EFAULT]
The numa_attr argument or the nattr_descr structure field points to an
invalid address.
[EINVAL]
The nattr_type field specifies an invalid resource type, the
nattr_descr field specifies an invalid resource, or the nattr_flags
field specifies an undefined flag.
[ENOMEM]
There is not enough memory to create the child process.
SEE ALSO
Functions: exec(2), exit(2), fork(2), mmap(2), plock(2), umask(2), nice(3),
nloc(3), nmmap(3), nsg_init(3), numa_intro(3), radsetops(3), ulimit(3)
Files: numa_types(4)
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