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    Subject[PATCH 0/3] compressed in-memory swapping take4

    Project home:

    It allows creating a RAM based block device which acts as swap disk.
    Pages swapped to this device are compressed and stored in memory itself.
    This is a big win over swapping to slow hard-disk which are typically used
    as swap disk. For flash, these suffer from wear-leveling issues when used
    as swap disk - so again its helpful. For swapless systems, it allows more
    apps to run.

    * Changelog: take4 vs take3
    xvmalloc changes:
    - Fixed regression in take3 that caused ramzswap write failures.
    This happened due to error in find_block() where we did not do
    explicit cast to 'unsigned long' when checking for bits set in
    bitmap. Now changed it to use kernel build-in test_bit().
    - Fix divide by zero error in proc read function.
    ramzswap changes:
    - Forward write requests to backing swap device if allocation for
    compressed page fails.
    - Code cleanups.

    (Please also see testing notes below).

    * Changelog: take3 vs take2
    xvmalloc changes:
    - Use kernel defined macros and constants in xvmalloc and remove
    equivalent defines for ALIGN, roundup etc.
    - Use kernel bitops (set_bit, clear_bit)
    - Moved it to drivers/block since its not clear if it has any other
    ramzswap changes:
    - All instances of compcache renamed to ramzswap.
    Also renamed module to ramzswap
    - Renamed "backing_dev" parameter to "backing_swap"
    - Documentation changes to reflect above changes.
    - Remove "table index" from object header (4 bytes). This will be
    needed when memory defragmentation is implemented. So, avoid this
    (small) overhead for now.

    * Changelog: take2 vs initial revision:
    xvmalloc changes:
    - Use Linux kernel coding style for xvmalloc
    - Collapse all individual flag test/set/get to generic {test_set_get}_flag
    - Added BLOCK_NEXT() macro to reach next contiguous block
    - Other minor cleanups - no functional changes
    compcache block device code:
    - compcache core changes due to change in xvmalloc interface names

    * Testing notes:
    - Multiple cycles of 'scan' benchmark available at:
    It does scans of anonymous mapped memory, both cyclic and use once.

    Arch: x86 and x64
    CPUs: 1/2, RAM: 512MB
    backing swap: 768MB, ramzswap memlimit: 76MB (15% of RAM).

    Continuously run 'scan' till it triggers 200K R/W operations on ramzswap.
    Any incompressible pages were correctly forwarded to backing swap device.
    cmd: ./scan 450 20 # scan over 450MB, 20 times.

    - Links to more performance numbers, use cases can be found at:

    Thanks to Ed Tomlinson for reporting bug in 'take3' patches
    and to reviewers of previous versions.


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