The mremap() function expands (or shrinks) an existing memory mapping, potentially moving it at the same time, depending on the flags argument and the available virtual address space.
old_address is the old address of the
virtual memory block to be resized.
old_address must be page aligned.
old_size is the old size of the virtual memory block.
new_size is the requested size of the
virtual memory block after the resize.
In Linux the memory is divided into pages. A user process has (one or) several linear virtual memory segments. Each virtual memory segment has one or more mappings to real memory pages (in the page table). Each virtual memory segment has its own protection (access rights), which may cause a segmentation violation if the memory is accessed incorrectly (e.g., writing to a read-only segment). Accessing virtual memory outside of the segments will also cause a segmentation violation.
mremap() uses the Linux page table scheme. mremap() changes the mapping between virtual addresses and memory pages. This can be used to implement a very efficient form of realloc().
The flags bit-mask argument may be 0, or include the following flag:
By default, if there is not sufficient space to expand a mapping at its current location, then mremap() fails. If this flag is specified, then the kernel is permitted to relocate the mapping to a new virtual address, if necessary. If the mapping is relocated, then absolute pointers into the old mapping location become invalid (offsets relative to the starting address of the mapping should be employed).
This flag serves a similar purpose to the
If the memory segment specified by
old_size is locked (using
mlock() or similar), then this lock is maintained
when the segment is resized and/or relocated. As a consequence, the
amount of memory locked by the process may change.
The mremap() function returns a pointer
to the new virtual memory area on success. On error, the value
MAP_FAILED is returned, and
is set appropriately.
The caller tried to expand a memory segment that is locked, but this was
not possible without exceeding the
"Segmentation fault." Some address in the range old_address to
An invalid argument was given. Possible causes are:
The memory area cannot be expanded at the current virtual address,