# alloc_hugepages

## NAME



           alloc_hugepages, free_hugepages - allocate or free huge pages
    


## SYNOPSIS



           **void *syscall(** size_t size;
                         **SYS_alloc_hugepages, int** _key_**, void** _addr_**[**_size_**], size_t** _size_**,**
                         **int** _prot_**, int** _flag_**);**
           **int syscall(SYS_free_hugepages, void ***_addr_**);**
    
           _Note_ : glibc provides no wrappers for these system calls,
           necessitating the use of syscall(2).
    


## DESCRIPTION



           The system calls **alloc_hugepages**() and **free_hugepages**() were
           introduced in Linux 2.5.36 and removed again in Linux 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 fail with the error **ENOSYS**.
    
           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.
    
           The _key_ 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 _key_ , and
           inherited by child processes.
    
           The _addr_ argument of **free_hugepages**() tells which page is being
           freed: it was the return value of a call to **alloc_hugepages**().
           (The memory is first actually freed when all users have released
           it.)  The _addr_ argument of **alloc_hugepages**() is a hint, that the
           kernel may or may not follow.  Addresses must be properly aligned.
    
           The _size_ argument is the size of the required segment.  It must be
           a multiple of the huge page size.
    
           The _prot_ argument specifies the memory protection of the segment.
           It is one of **PROT_READ** , **PROT_WRITE** , **PROT_EXEC**.
    
           The _flag_ argument is ignored, unless _key_ is positive.  In that
           case, if _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 returned when no segment with the given key
           exists.
    


## RETURN VALUE



           On success, **alloc_hugepages**() returns the allocated virtual
           address, and **free_hugepages**() returns zero.  On error, -1 is
           returned, and _errno_ is set to indicate the error.
    


## ERRORS



           **ENOSYS** The system call is not supported on this kernel.
    


## FILES



           _/proc/sys/vm/nr_hugepages_
                  Number of configured hugetlb pages.  This can be read and
                  written.
    
           _/proc/meminfo_
                  Gives info on the number of configured hugetlb pages and on
                  their size in the three variables HugePages_Total,
                  HugePages_Free, Hugepagesize.
    


## STANDARDS



           Linux on Intel processors.
    


## NOTES



           Now the hugetlbfs filesystem can be used instead.  Memory backed
           by huge pages (if the CPU supports them) is obtained by using
           mmap(2) to map files in this virtual filesystem.
    
           The maximal number of huge pages can be specified using the
           **hugepages=** boot parameter.
    


* * *