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    SubjectRe: [git patches] xfs and block fixes for virtually indexed arches
    On Fri, Dec 18, 2009 at 09:21:30AM +0900, FUJITA Tomonori wrote:
    > iSCSI initiator driver should work with kmalloc'ed memory.
    > The reason why iSCSI didn't work with kmalloc'ed memory is that it
    > uses sendpage (which needs refcountable pages). We added a workaround
    > to not use sendpage with kmalloc'ed memory (it would be great if we
    > remove the workaround though).

    Well, with a patch that I plan to be pushing that we have general
    agreement that it is a block device driver BUG not to accept
    kmalloc'ed/SLAB allocated memory, is one where ext4 will use
    kmalloc'ed/slab allocated memory on occasion when it needs to make
    shadow copy of buffers for journalling purposes AND when the fs block
    size is smaller than the page size. (i.e., no more allocating a 16k
    page when the fs block size is 4k). So this won't happen all the
    time; even if the case of a 16k Itanium system with 4k blocks, the
    bulk of the data won't be sent via kmalloc'ed memory --- just some
    critical metadata block and some data blocks that need to be escaped
    when being written into the journal.

    I do think we need to document that block device drivers are
    _expected_ to be able to handle kmalloc'ed memory, and if they can't,
    #1 they should do a BUG_ON instead of corrupting user's data, and #2,
    if they do corrupt data, we should send the angry users with corrupted
    file systems to bang at the doors of the block device authors.

    - Ted

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