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    SubjectRe: [PATCH 00/11] Add compression support to pstore
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    On Tue, Aug 6, 2013 at 10:35 PM, Tony Luck <tony.luck@gmail.com> wrote:
    > ERST is at the whim of the BIOS writer (the ACPI standard doesn't provide any
    > suggestions on record sizes). My systems support ~6K record size.

    Off by a little - 7896 bytes on my current machine.

    > efivars has, IIRC, a 1k limit coded in the Linux back end.
    My memory was correct for this one.

    Adding a little tracing to pstore_getrecords() I see this:

    pstore: inflated 3880 bytes compressed to 17459 bytes
    pstore: inflated 2567 bytes compressed to 17531 bytes
    pstore: inflated 4018 bytes compressed to 17488 bytes

    Which isn't at all what I expected. The ERST backend
    advertised a bufsize of 7896, and I have the default
    kmsg_bytes of 10240. So on my forced panic the code
    decided to create a three part pstore dump. The sum of
    the pieces is close to, but a little over the target of 10K.
    But I don't understand why the compressed sizes are so
    much smaller that the ERST backend block size.

    The uncompressed sizes appear to be close to constant.
    The compression ratios vary from 14% to 23%

    Why do we get three small parts instead of two bigger
    ones close the the 7896 ERST bufsize?

    -Tony


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