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   xfs_io    ( 8 )

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MEMORY MAPPED I/O COMMANDS

mmap [ N | [[ -rwxS ] [-s size ] offset length ]] With no arguments, mmap shows the current mappings. Specifying a single numeric argument N sets the current mapping. If two arguments are specified (a range specified by offset and length), a new mapping is created spanning the range, and the protection mode can be given as a combination of PROT_READ (-r), PROT_WRITE (-w), and PROT_EXEC (-x). The mapping will be created with the MAP_SHARED flag by default, or with the Linux specific (MAP_SYNC | MAP_SHARED_VALIDATE) flags if -S is given. -s size is used to do a mmap(size) && munmap(size) operation at first, try to reserve some extendible free memory space, if size is bigger than length parameter. But there's not guarantee that the memory after length ( up to size ) will stay free. e.g. "mmap -rw -s 8192 1024" will mmap 0 ~ 1024 bytes memory, but try to reserve 1024 ~ 8192 free space(no guarantee). This free space will helpful for "mremap 8192" without MREMAP_MAYMOVE flag.

mm See the mmap command.

mremap [ -f <new_address> ] [ -m ] new_length Changes the current mapping size to new_length. Whether the mapping may be moved is controlled by the flags passed; MREMAP_FIXED (-f), or MREMAP_MAYMOVE (-m). new_length specifies a page-aligned address to which the mapping must be moved. It can be set to 139946004389888, 4096k or 1g etc.

mrm See the mremap command.

munmap Unmaps the current memory mapping.

mu See the munmap command.

mread [ -f | -v ] [ -r ] [ offset length ] Accesses a segment of the current memory mapping, optionally dumping it to the standard output stream (with -v or -f option) for inspection. The accesses are performed sequentially from the start offset by default, but can also be done from the end backwards through the mapping if the -r option in specified. The two verbose modes differ only in the relative offsets they display, the -f option is relative to file start, whereas -v shows offsets relative to the start of the mapping.

mr See the mread command.

mwrite [ -r ] [ -S seed ] [ offset length ] Stores a byte into memory for a range within a mapping. The default stored value is 'X', repeated to fill the range specified, but this can be changed using the -S option. The memory stores are performed sequentially from the start offset by default, but can also be done from the end backwards through the mapping if the -r option in specified.

mw See the mwrite command.

msync [ -i ] [ -a | -s ] [ offset length ] Writes all modified copies of pages over the specified range (or entire mapping if no range specified) to their backing storage locations. Also, optionally invalidates (-i) so that subsequent references to the pages will be obtained from their backing storage locations (instead of cached copies). The flush can be done synchronously (-s) or asynchronously (-a).

ms See the msync command.

madvise [ -d | -r | -s | -w ] [ offset length ] Modifies page cache behavior when operating on the current mapping. The range arguments are required by some advise commands ([*] below). With no arguments, the POSIX_MADV_NORMAL advice is implied (default readahead). -d the pages will not be needed (POSIX_MADV_DONTNEED[*]). -r expect random page references (POSIX_MADV_RANDOM), which sets readahead to zero. -s expect sequential page references (POSIX_MADV_SEQUENTIAL), which doubles the default readahead on the file. -w advises the specified pages will be needed again (POSIX_MADV_WILLNEED[*]) which forces the maximum readahead.

mincore Dumps a list of pages or ranges of pages that are currently in core, for the current memory mapping.