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    SubjectRe: [RFC] block integrity: Fix write after checksum calculation problem
    >>>>> "Dave" == Dave Chinner <> writes:

    >> Agreed. I too am curious to study which circumstances favor copying
    >> vs blocking.

    Dave> IMO blocking is generally preferable in high throughput threaded
    Dave> workloads as there is always another thread that can do useful
    Dave> work while we wait for IO to complete. Most use cases for DIF
    Dave> center around high throughput environments....


    A while back I did a bunch of tests with a liberal amount of
    wait_on_page_writeback() calls added to (I think) ext2, ext3, and
    XFS. For my regular workloads there was no measurable change (kernel
    builds, random database and I/O tests). I'm sure we'll unearth some apps
    that will suffer when DI is on but so far I'm not too worried about
    blocking in the data path.

    My main concern is wrt. metadata because that's where extN really
    hurts. Simple test: Unpack a kernel tarball and watch the directory
    block fireworks. Given how frequently those buffers get hit I'm sure
    blocking would cause performance to tank completely. I looked into
    fixing this in ext2 but I had to stop because my eyes were bleeding.

    Martin K. Petersen Oracle Linux Engineering

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