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    Subject[PATCH v5 0/4] zram memory tracking
    Date
    zRam as swap is useful for small memory device. However, swap means
    those pages on zram are mostly cold pages due to VM's LRU algorithm.
    Especially, once init data for application are touched for launching,
    they tend to be not accessed any more and finally swapped out.
    zRAM can store such cold pages as compressed form but it's pointless
    to keep in memory. As well, it's pointless to store incompressible
    pages to zram so better idea is app developers manages them directly
    like free or mlock rather than remaining them on heap.

    This patch provides a debugfs /sys/kernel/debug/zram/zram0/block_state
    to represent each block's state so admin can investigate what memory is
    cold|incompressible|same page with using pagemap once the pages are
    swapped out.


    The output is as follows,
    300 75.033841 .wh
    301 63.806904 s..
    302 63.806919 ..h

    First column is zram's block index and 3rh one represents symbol
    (s: same page w: written page to backing store h: huge page) of the
    block state. Second column represents usec time unit of the block
    was last accessed. So above example means the 300th block is accessed
    at 75.033851 second and it was huge so it was written to the backing
    store.

    * from v4:
    * Fix typos - Randy
    * Add reviewed-by from Sergey

    * from v3:
    * use depends on selecting DEBUG_FS - Greg KH
    * Add acked-by from Greg
    * Fix null ptr access at module unload - Sergey
    * warning fix from copy_to_user - Sergey

    * From v2:
    * debugfs and Kconfig cleanup - Greg KH
    * Remove unnecesarry buffer - Sergey
    * Change timestamp from sec to usec

    * From v1:
    * Do not propagate error number for debugfs fail - Greg KH
    * Add writeback and hugepage information - Serge

    Minchan Kim (4):
    zram: correct flag name of ZRAM_ACCESS
    zram: mark incompressible page as ZRAM_HUGE
    zram: record accessed second
    zram: introduce zram memory tracking

    Documentation/blockdev/zram.txt | 25 +++++
    drivers/block/zram/Kconfig | 14 ++-
    drivers/block/zram/zram_drv.c | 173 +++++++++++++++++++++++++++++---
    drivers/block/zram/zram_drv.h | 14 ++-
    4 files changed, 207 insertions(+), 19 deletions(-)

    --
    2.17.0.484.g0c8726318c-goog

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