Re: mmap visited files?

Re: mmap visited files?

[Richard Stallman]

    I use mmap-ed data files in my gps-mapping program and there is
    another big win if one plays one's cards right: free autosaves.  In my
    case I temporarily append stuff to the end of the mmap-ed file.  If
    the program crashes, the data in the mmaped buffers still gets flushed
    to the underlying disk file by the OS.  It sure beats complex autosave
    logic.  It might be worth trying a similar hack for emacs -- mmap the
    single-gap buffer directly into a temporary file.

This might possibly be a good idea.  It could not replace the current
auto-save feature, because the mmap'd file would have a gap in it and
it would not be possible to record where that is.  Also, the pages may
not necessarily be saved at the same time.  So it would take hand
editing to use this file for recovery.  But it might be useful
nonetheless.

The question is how much additional value this would give beyond the
existing auto save feature.  Maybe not much.

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Re: mmap visited files?

[Ken Raeburn]

There's a risk with using mmap: If the file is truncated for some
reason, the mapped pages may no longer be useable, and references to
them may crash the program.  (I investigated this a little while I was
working on binutils.)  Perhaps that wouldn't happen often, but
deleting autosave files to gain a little bit of space on a nearly-full
file system does happen....

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