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    SubjectRe: ramdisk corruption problems - was: RE: pivot_root and initrd kern el panic woes


    On Sat, 29 Dec 2001, Andrew Morton wrote:

    > Would it be necessary to preallocate the holes at mmap() time? Mad
    > hand-waving: Could we not perform the instantiation at pagefault time,
    > and give the caller SIGBUS if we cannot allocate the blocks? Or if
    > there's an IO error, or quota exceeded.

    Allocation at mmap() Is Not Going To Happen. Consider it vetoed.
    There are applications that use mmap() on large and very sparse
    files.

    > Question: can someone please define BH_New? Its lifecycle seems
    > very vague. We never actually seem to *clear* it anywhere for
    > ext2, and it appears that the kernel will keep on treating a
    > clearly non-new buffer as "new" all the time. ext3 explicitly
    > clears BH_New in get_block(), if it finds the block was already
    > present in the file. I did this because we need the newness
    > info for internal purposes.

    It should be reset when we submit IO. Breakage related to failing
    allocation is indeed not new, but that's a long story. And no,
    "allocate on mmap()" is not a fix.

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