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    SubjectRe: ramdisk corruption problems - was: RE: pivot_root and initrd kern el panic woes
    On Sat, Dec 29, 2001 at 10:38:14PM -0800, Andrew Morton wrote:
    > 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

    see the other email, it's all right as far I can tell, it doesn't need
    to be resetted ever. only mapped bh are bh_new so you will never care
    about bh_new any longer because you will never need any further
    get_block on the same bh.

    > 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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