[lkml]   [2000]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: mmap/munmap semantics

    On Tue, 22 Feb 2000 18:46:02 +0100 (MET), Richard Guenther
    <> said:

    > 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,

    All file contents default to zero anyway, so just ftruncate() the file
    to create as much demand-zeroed mmapable memory as you want.

    > - 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.

    The only way is to use Chuck Lever's madvise() patches:
    madvise(MADV_DONTNEED) is exactly what you need there. It's not yet in
    Linus's 2.3 tree, but the API is pretty standard.

    > Ideally a hole could be created in the mmapped file on drop time -

    No, if the mmaped area has already been flushed to disk then there is no
    way at all to recreate the hole except by truncating and then
    re-extending the file (which destroys everything until EOF, of course).


    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:56    [W:0.021 / U:5.676 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site