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    Subject[PATCH 0/7 v2] More graceful flusher thread memory reclaim wakeup
    Date
    We've had some issues with writeback in presence of memory reclaim
    at Facebook, and this patch set attempts to fix it up. The real
    functional change is the last patch in the series, the first 5 are
    prep and cleanup patches.

    The basic idea is that we have callers that call
    wakeup_flusher_threads() with nr_pages == 0. This means 'writeback
    everything'. For memory reclaim situations, we can end up queuing
    a TON of these kinds of writeback units. This can cause softlockups
    and further memory issues, since we allocate huge amounts of
    struct wb_writeback_work to handle this writeback. Handle this
    situation more gracefully.

    Changes since v1:

    - Rename WB_zero_pages to WB_start_all (Amir).
    - Remove a test_bit() for a condition where we always expect the bit
    to be set.
    - Remove 'nr_pages' from the wakeup flusher threads helpers, since
    everybody now passes in zero. Enables further cleanups in later
    patches too (Jan).
    - Fix a case where I forgot to clear WB_start_all if 'work' allocation
    failed.
    - Get rid of cond_resched() in the wb_do_writeback() loop.

    --
    Jens Axboe


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