1ALLOC_HUGEPAGES(2)         Linux Programmer's Manual        ALLOC_HUGEPAGES(2)
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NAME

6       alloc_hugepages, free_hugepages - allocate or free huge pages
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SYNOPSIS

9       void *syscall(SYS_alloc_hugepages, int key, void *addr, size_t len,
10                     int prot, int flag);
11       int syscall(SYS_free_hugepages, void *addr);
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13       Note:  glibc provides no wrappers for these system calls, necessitating
14       the use of syscall(2).
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DESCRIPTION

17       The system calls alloc_hugepages() and free_hugepages() were introduced
18       in Linux 2.5.36 and removed again in 2.5.54.  They existed only on i386
19       and ia64 (when built with CONFIG_HUGETLB_PAGE).  In Linux  2.4.20,  the
20       syscall numbers exist, but the calls fail with the error ENOSYS.
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22       On  i386  the  memory  management  hardware  knows about ordinary pages
23       (4 KiB) and huge pages (2 or 4 MiB).  Similarly ia64 knows  about  huge
24       pages  of  several  sizes.   These system calls serve to map huge pages
25       into the process's memory or to free them again.  Huge pages are locked
26       into memory, and are not swapped.
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28       The  key  argument  is an identifier.  When zero the pages are private,
29       and not inherited by children.  When positive the pages are shared with
30       other  applications  using  the  same  key, and inherited by child pro‐
31       cesses.
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33       The addr argument of free_hugepages() tells which page is being  freed:
34       it was the return value of a call to alloc_hugepages().  (The memory is
35       first actually freed when all users have released it.)  The addr  argu‐
36       ment  of  alloc_hugepages()  is  a hint, that the kernel may or may not
37       follow.  Addresses must be properly aligned.
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39       The len argument is the length of the required segment.  It must  be  a
40       multiple of the huge page size.
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42       The  prot  argument specifies the memory protection of the segment.  It
43       is one of PROT_READ, PROT_WRITE, PROT_EXEC.
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45       The flag argument is ignored, unless key is positive.  In that case, if
46       flag  is  IPC_CREAT,  then a new huge page segment is created when none
47       with the given key existed.  If this flag is not set,  then  ENOENT  is
48       returned when no segment with the given key exists.
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RETURN VALUE

51       On  success,  alloc_hugepages()  returns the allocated virtual address,
52       and free_hugepages() returns zero.  On error, -1 is returned, and errno
53       is set to indicate the error.
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ERRORS

56       ENOSYS The system call is not supported on this kernel.
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FILES

59       /proc/sys/vm/nr_hugepages
60              Number  of configured hugetlb pages.  This can be read and writ‐
61              ten.
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63       /proc/meminfo
64              Gives info on the number of  configured  hugetlb  pages  and  on
65              their    size    in   the   three   variables   HugePages_Total,
66              HugePages_Free, Hugepagesize.
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CONFORMING TO

69       These extinct system calls were specific to Linux on Intel processors.
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NOTES

72       These system calls are gone; they existed only in Linux 2.5.36  through
73       to  2.5.54.   Now the hugetlbfs filesystem can be used instead.  Memory
74       backed by huge pages (if the CPU supports them) is  obtained  by  using
75       mmap(2) to map files in this virtual filesystem.
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77       The  maximal number of huge pages can be specified using the hugepages=
78       boot parameter.
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COLOPHON

81       This page is part of release 5.12 of the Linux  man-pages  project.   A
82       description  of  the project, information about reporting bugs, and the
83       latest    version    of    this    page,    can     be     found     at
84       https://www.kernel.org/doc/man-pages/.
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88Linux                             2021-03-22                ALLOC_HUGEPAGES(2)
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