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Diffstat (limited to 'Documentation/vm/hugetlbpage.txt')
| -rw-r--r-- | Documentation/vm/hugetlbpage.txt | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/Documentation/vm/hugetlbpage.txt b/Documentation/vm/hugetlbpage.txt index 1ad9af1ca4d..687104bfd09 100644 --- a/Documentation/vm/hugetlbpage.txt +++ b/Documentation/vm/hugetlbpage.txt @@ -27,12 +27,21 @@ number of free hugetlb pages at any time. It also displays information about the configured hugepage size - this is needed for generating the proper alignment and size of the arguments to the above system calls. -The output of "cat /proc/meminfo" will have output like: +The output of "cat /proc/meminfo" will have lines like: ..... HugePages_Total: xxx HugePages_Free: yyy -Hugepagesize: zzz KB +HugePages_Rsvd: www +Hugepagesize: zzz kB + +where: +HugePages_Total is the size of the pool of hugepages. +HugePages_Free is the number of hugepages in the pool that are not yet +allocated. +HugePages_Rsvd is short for "reserved," and is the number of hugepages +for which a commitment to allocate from the pool has been made, but no +allocation has yet been made. It's vaguely analogous to overcommit. /proc/filesystems should also show a filesystem of type "hugetlbfs" configured in the kernel. @@ -42,11 +51,11 @@ pages in the kernel. Super user can dynamically request more (or free some pre-configured) hugepages. The allocation (or deallocation) of hugetlb pages is possible only if there are enough physically contiguous free pages in system (freeing of hugepages is -possible only if there are enough hugetlb pages free that can be transfered +possible only if there are enough hugetlb pages free that can be transferred back to regular memory pool). -Pages that are used as hugetlb pages are reserved inside the kernel and can -not be used for other purposes. +Pages that are used as hugetlb pages are reserved inside the kernel and cannot +be used for other purposes. Once the kernel with Hugetlb page support is built and running, a user can use either the mmap system call or shared memory system calls to start using @@ -60,7 +69,7 @@ Use the following command to dynamically allocate/deallocate hugepages: This command will try to configure 20 hugepages in the system. The success or failure of allocation depends on the amount of physically contiguous memory that is preset in system at this time. System administrators may want -to put this command in one of the local rc init file. This will enable the +to put this command in one of the local rc init files. This will enable the kernel to request huge pages early in the boot process (when the possibility of getting physical contiguous pages is still very high). @@ -78,8 +87,8 @@ the uid and gid of the current process are taken. The mode option sets the mode of root of file system to value & 0777. This value is given in octal. By default the value 0755 is picked. The size option sets the maximum value of memory (huge pages) allowed for that filesystem (/mnt/huge). The size is -rounded down to HPAGE_SIZE. The option nr_inode sets the maximum number of -inodes that /mnt/huge can use. If the size or nr_inode options are not +rounded down to HPAGE_SIZE. The option nr_inodes sets the maximum number of +inodes that /mnt/huge can use. If the size or nr_inodes options are not provided on command line then no limits are set. For size and nr_inodes options, you can use [G|g]/[M|m]/[K|k] to represent giga/mega/kilo. For example, size=2K has the same meaning as size=2048. An example is given at @@ -88,7 +97,7 @@ the end of this document. read and write system calls are not supported on files that reside on hugetlb file systems. -A regular chown, chgrp and chmod commands (with right permissions) could be +Regular chown, chgrp, and chmod commands (with right permissions) could be used to change the file attributes on hugetlbfs. Also, it is important to note that no such mount command is required if the @@ -96,8 +105,8 @@ applications are going to use only shmat/shmget system calls. Users who wish to use hugetlb page via shared memory segment should be a member of a supplementary group and system admin needs to configure that gid into /proc/sys/vm/hugetlb_shm_group. It is possible for same or different -applications to use any combination of mmaps and shm* calls. Though the -mount of filesystem will be required for using mmaps. +applications to use any combination of mmaps and shm* calls, though the +mount of filesystem will be required for using mmap calls. ******************************************************************* |