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    SubjectRe: [RFC] delayed allocation for ext4
    On Sat, Dec 23, 2006 at 10:09:57PM +0300, Alex Tomas wrote:
    >
    > Good day,
    >
    > >>>>> David Chinner (DC) writes:
    >
    > DC> So that mean's we'll have 2 separate mechanisms for marking
    > DC> pages as delalloc. XFS uses the BH_delay flag to indicate
    > DC> that a buffer (block) attached to the page is using delalloc.
    >
    > well, for blocksize=pagesize we can save 56 bytes on every page.

    Sure, but it means that ext4 w/ delalloc won't work on lots of
    machines....

    > DC> FWIW, how does this mechanism deal with block size < page size?
    > DC> Don't you have to track delalloc on a block basis rather than
    > DC> a page basis?
    >
    > I'm still thinking how better to deal with that w/o much code duplication.

    Code duplication in ext4, or across all filesystems?

    > DC> Ah, that's why you can get away with a page flag - you've ignored
    > DC> the partial page delay state problem. Any plans to use the
    > DC> existing method in the future so we will be able to use ext4 delalloc
    > DC> on machines with a page size larger than 4k?
    >
    > what do you mean by "exsiting"? BH_delay?

    Yes.

    Cheers,

    Dave.
    --
    Dave Chinner
    Principal Engineer
    SGI Australian Software Group
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