Manpage of ALLOC_HUGEPAGES
ALLOC_HUGEPAGESSection: Linux Programmer's Manual (2)
NAMEalloc_hugepages, free_hugepages - allocate or free huge pages
void *alloc_hugepages(int key, void *addr, size_t len, int prot, int flag);int free_hugepages(void *addr);
DESCRIPTIONThe system calls alloc_hugepages() and 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 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 keyargument 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 addrargument 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 addrargument of alloc_hugepages() is a hint, that the kernel may or may not follow. Addresses must be properly aligned.
The lenargument is the length of the required segment. It must be a multiple of the huge page size.
The protargument specifies the memory protection of the segment. It is one of PROT_READ, PROT_WRITE, PROT_EXEC.
The flagargument is ignored, unless keyis positive. In that case, if flagis IPC_CREAT, then a new huge page segment is created when none with the given key existed. If this flag is not set, then ENOENTis returned when no segment with the given key exists.
RETURN VALUEOn success, alloc_hugepages() returns the allocated virtual address, and free_hugepages() returns zero. On error, -1 is returned, and errnois set appropriately.
- The system call is not supported on this kernel.
FILES/proc/sys/vm/nr_hugepagesNumber of configured hugetlb pages. This can be read and written.
CONFORMING TOThese calls are specific to Linux on Intel processors, and should not be used in programs intended to be portable.
NOTESThese 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 using mmap(2) to map files in this virtual filesystem.
The maximal number of huge pages can be specified using the hugepages=boot parameter.
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