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    SubjectRe: ramdisk corruption problems - was: RE: pivot_root and initrd kern el panic woes
    Alexander Viro wrote:
    >
    > 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.

    I think Andrea was referring to simply reserving the necessary
    amount of disk space, rather than actually instantiating the
    blocks. But even that would be a big problem for the applications
    which you describe.

    > > 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.

    well... It isn't. And I'd like a chance to review/test any
    proposed changes in this area which are outside specific filesystems...

    > Breakage related to failing allocation is indeed not new, but
    > that's a long story. And no, "allocate on mmap()" is not a fix.

    Yup. But what *is* the fix? (filemap_nopage?)

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