Richard Guenther writes:
> Hi!
>
> With the ongoing development of GLAME there arise the following
> problems with the backing-store management, which is a mmaped
> file and does "userspace virtual memory management":
> - I cannot see a way to mmap a part of the file but set the
> contents initially to zero, i.e. I want to setup an initially
> dirty zero-mapping which is assigned to a part of the file.
> Currently I'm just mmaping the part and do the zeroing by
> reading from /dev/zero (which does as I understand from the
> kernel code just create this zero mappings) - is there a more
> portable way to achieve this?
> - I need to "drop" a mapping sometimes without writing the contents
> back to disk - I cannot see a way to do this with linux currently.
> Ideally a hole could be created in the mmapped file on drop time -
> is this possible at all with the VFS/ext2 at the moment (creating
> a hole in a file by dropping parts of it)?
>
> So for the first case we could add a flag to mmap like MAP_ZERO to
> indicate a zero-map (dirty).
>
> For the second case either the munmap call needs to be extended or
> some sort of madvise with a MADV_CLEAN flag? Or we can just adjust
> mprotect(PROT_NONE) and subsequent munmap() to do the dropping?
Maybe you can make use of the same driver that I'd like to use:
- a processes opens the driver device file, and passes the FD to
another "daemon" process (a child or whatever)
- one process mmap(2)s the FD and does reads and writes to the VMA
- the "daemon" does an ioctl(2) waiting for page fault events, and
proceeds to read(2)/write(2) to satisfy the page faults
- the driver passes page fault and free memory request events to the
daemon.
This allows you to set up a user-space virtual memory system. This is
useful for me, it may be useful for you.
All I need to do is find a victim to volunteer to write this ;-)
Regards,
Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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This archive was generated by hypermail 2b29 : Wed Feb 23 2000 - 21:00:31 EST