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hugetlb: add MAP_HUGETLB example
Add an example of how to use the MAP_HUGETLB flag to the vm documentation directory and a reference to the example in hugetlbpage.txt. Signed-off-by: Eric B Munson <ebmunson@us.ibm.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Adam Litke <agl@us.ibm.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -22,3 +22,5 @@ slabinfo.c
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- source code for a tool to get reports about slabs.
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slub.txt
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- a short users guide for SLUB.
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map_hugetlb.c
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- an example program that uses the MAP_HUGETLB mmap flag.
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@ -187,12 +187,14 @@ Regular chown, chgrp, and chmod commands (with right permissions) could be
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used to change the file attributes on hugetlbfs.
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Also, it is important to note that no such mount command is required if the
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applications are going to use only shmat/shmget system calls. Users who
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wish to use hugetlb page via shared memory segment should be a member of
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a supplementary group and system admin needs to configure that gid into
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/proc/sys/vm/hugetlb_shm_group. It is possible for same or different
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applications to use any combination of mmaps and shm* calls, though the
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mount of filesystem will be required for using mmap calls.
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applications are going to use only shmat/shmget system calls or mmap with
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MAP_HUGETLB. Users who wish to use hugetlb page via shared memory segment
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should be a member of a supplementary group and system admin needs to
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configure that gid into /proc/sys/vm/hugetlb_shm_group. It is possible for
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same or different applications to use any combination of mmaps and shm*
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calls, though the mount of filesystem will be required for using mmap calls
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without MAP_HUGETLB. For an example of how to use mmap with MAP_HUGETLB see
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map_hugetlb.c.
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*******************************************************************
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77
Documentation/vm/map_hugetlb.c
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77
Documentation/vm/map_hugetlb.c
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@ -0,0 +1,77 @@
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/*
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* Example of using hugepage memory in a user application using the mmap
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* system call with MAP_HUGETLB flag. Before running this program make
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* sure the administrator has allocated enough default sized huge pages
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* to cover the 256 MB allocation.
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*
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* For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
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* That means the addresses starting with 0x800000... will need to be
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* specified. Specifying a fixed address is not required on ppc64, i386
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* or x86_64.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <fcntl.h>
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#define LENGTH (256UL*1024*1024)
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#define PROTECTION (PROT_READ | PROT_WRITE)
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#ifndef MAP_HUGETLB
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#define MAP_HUGETLB 0x40
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#endif
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/* Only ia64 requires this */
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#ifdef __ia64__
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#define ADDR (void *)(0x8000000000000000UL)
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#define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_FIXED)
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#else
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#define ADDR (void *)(0x0UL)
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#define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)
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#endif
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void check_bytes(char *addr)
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{
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printf("First hex is %x\n", *((unsigned int *)addr));
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}
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void write_bytes(char *addr)
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{
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unsigned long i;
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for (i = 0; i < LENGTH; i++)
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*(addr + i) = (char)i;
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}
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void read_bytes(char *addr)
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{
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unsigned long i;
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check_bytes(addr);
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for (i = 0; i < LENGTH; i++)
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if (*(addr + i) != (char)i) {
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printf("Mismatch at %lu\n", i);
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break;
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}
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}
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int main(void)
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{
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void *addr;
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addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, 0, 0);
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if (addr == MAP_FAILED) {
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perror("mmap");
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exit(1);
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}
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printf("Returned address is %p\n", addr);
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check_bytes(addr);
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write_bytes(addr);
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read_bytes(addr);
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munmap(addr, LENGTH);
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return 0;
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}
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