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Re: Some memory reallocation in kernel mode

> 	kmalloc is allocation. what i want to know is - what realloc does in
> user space, is there something like that in kernel space. or i have to
> do manually. 

It's probably something you don't want to attempt. Here is a comment
from glibc sources.

Having a device driver copy "unknown" amounts of data doesn't sound
very familiar to me. Perhaps there is a way to configure your hardware
to copy data in fixed size chunks ?



  Realloc algorithm:

    Chunks that were obtained via mmap cannot be extended or shrunk
    unless HAVE_MREMAP is defined, in which case mremap is used.
    Otherwise, if their reallocation is for additional space, they are
    copied.  If for less, they are just left alone.

    Otherwise, if the reallocation is for additional space, and the
    chunk can be extended, it is, else a malloc-copy-free sequence is
    taken.  There are several different ways that a chunk could be
    extended. All are tried:

       * Extending forward into following adjacent free chunk.
       * Shifting backwards, joining preceding adjacent space
       * Both shifting backwards and extending forward.
       * Extending into newly sbrked space

    Unless the #define REALLOC_ZERO_BYTES_FREES is set, realloc with a
    size argument of zero (re)allocates a minimum-sized chunk.

    If the reallocation is for less space, and the new request is for
    a `small' (<512 bytes) size, then the newly unused space is lopped
    off and freed.

    The old unix realloc convention of allowing the last-free'd chunk
    to be used as an argument to realloc is no longer supported.
    I don't know of any programs still relying on this feature,
    and allowing it would also allow too many other incorrect
    usages of realloc to be sensible.