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-.TH ALLOC_HUGEPAGES 2 2003-02-02 "Linux 2.5.36" "Linux Programmer's Manual"
+.TH ALLOC_HUGEPAGES 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
alloc_hugepages, free_hugepages \- allocate or free huge pages
.SH SYNOPSIS
-.BI "void *alloc_hugepages(int " key ", void *" addr ", size_t " len ", int " prot ", int " flag );
+.nf
+.BI "void *alloc_hugepages(int " key ", void *" addr ", size_t " len ,
+.BI " int " prot ", int " flag );
.\" asmlinkage unsigned long sys_alloc_hugepages(int key, unsigned long addr,
.\" unsigned long len, int prot, int flag);
-.sp
+.PP
.BI "int free_hugepages(void *" addr );
.\" asmlinkage int sys_free_hugepages(unsigned long addr);
+.fi
.SH DESCRIPTION
The system calls
.BR alloc_hugepages ()
and
.BR free_hugepages ()
were introduced in Linux 2.5.36 and removed again in 2.5.54.
-They existed only on i386 and ia64 (when built with CONFIG_HUGETLB_PAGE).
-In Linux 2.4.20 the syscall numbers exist, but the calls return ENOSYS.
-.LP
-On i386 the memory management hardware knows about ordinary pages (4 KiB)
-and huge pages (2 or 4 MiB). Similarly ia64 knows about huge pages of
-several sizes. These system calls serve to map huge pages into the
-process' memory or to free them again.
+They existed only on i386 and ia64 (when built with
+.BR CONFIG_HUGETLB_PAGE ).
+In Linux 2.4.20, the syscall numbers exist,
+but the calls fail with the error
+.BR ENOSYS .
+.PP
+On i386 the memory management hardware knows about ordinary pages (4\ KiB)
+and huge pages (2 or 4\ MiB).
+Similarly ia64 knows about huge pages of
+several sizes.
+These system calls serve to map huge pages into the
+process's memory or to free them again.
Huge pages are locked into memory, and are not swapped.
-.LP
+.PP
The
.I key
-parameter is an identifier. When zero the pages are private, and
+argument is an identifier.
+When zero the pages are private, and
not inherited by children.
When positive the pages are shared with other applications using the same
.IR key ,
and inherited by child processes.
-.LP
+.PP
The
.I addr
-parameter of
-.B free_hugepages()
+argument of
+.BR free_hugepages ()
tells which page is being freed: it was the return value of a
call to
-.BR alloc_hugepages() .
+.BR alloc_hugepages ().
(The memory is first actually freed when all users have released it.)
The
.I addr
-parameter of
-.B alloc_hugepages()
+argument of
+.BR alloc_hugepages ()
is a hint, that the kernel may or may not follow.
Addresses must be properly aligned.
-.LP
+.PP
The
.I len
-parameter is the length of the required segment. It must be
-a multiple of the huge page size.
-.LP
+argument is the length of the required segment.
+It must be a multiple of the huge page size.
+.PP
The
.I prot
-parameter specifies the memory protection of the segment.
-It is one of PROT_READ, PROT_WRITE, PROT_EXEC.
-.LP
+argument specifies the memory protection of the segment.
+It is one of
+.BR PROT_READ ,
+.BR PROT_WRITE ,
+.BR PROT_EXEC .
+.PP
The
.I flag
-parameter is ignored, unless
+argument is ignored, unless
.I key
-is positive. In that case, if
+is positive.
+In that case, if
.I flag
-is IPC_CREAT, then a new huge page segment is created when none
-with the given key existed. If this flag is not set, then ENOENT
+is
+.BR IPC_CREAT ,
+then a new huge page segment is created when none
+with the given key existed.
+If this flag is not set, then
+.B ENOENT
is returned when no segment with the given key exists.
-.IR
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success,
.BR alloc_hugepages ()
returns the allocated virtual address, and
.BR free_hugepages ()
-returns zero. On error, \-1 is returned, and
+returns zero.
+On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B ENOSYS
The system call is not supported on this kernel.
-.SH "CONFORMING TO"
-These calls existed only in Linux 2.5.36 through to 2.5.54.
-These calls are specific to Linux on Intel processors, and should not be
-used in programs intended to be portable. Indeed, the system call numbers
-are marked for reuse, so programs using these may do something random
-on a future kernel.
.SH FILES
+.TP
.I /proc/sys/vm/nr_hugepages
Number of configured hugetlb pages.
This can be read and written.
-.LP
+.TP
.I /proc/meminfo
Gives info on the number of configured hugetlb pages and on their size
in the three variables HugePages_Total, HugePages_Free, Hugepagesize.
+.SH CONFORMING TO
+These calls are specific to Linux on Intel processors, and should not be
+used in programs intended to be portable.
.SH NOTES
-The system calls are gone. Now the hugetlbfs filesystem can be used instead.
+These system calls are gone;
+they existed only in Linux 2.5.36 through to 2.5.54.
+Now the hugetlbfs filesystem can be used instead.
Memory backed by huge pages (if the CPU supports them) is obtained by
-mmap'ing files in this virtual filesystem.
-.LP
+using
+.BR mmap (2)
+to map files in this virtual filesystem.
+.PP
The maximal number of huge pages can be specified using the
.B hugepages=
boot parameter.
-
+.PP
.\" requires CONFIG_HUGETLB_PAGE (under "Processor type and features")
.\" and CONFIG_HUGETLBFS (under "Filesystems").
.\" mount -t hugetlbfs hugetlbfs /huge
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