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    SubjectRe: [PATCH 0/6] More graceful flusher thread memory reclaim wakeup
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    On 09/20/2017 01:29 PM, John Stoffel wrote:
    > On Tue, Sep 19, 2017 at 01:53:01PM -0600, Jens Axboe wrote:
    >> 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.
    >
    > This looks nice, but do you have any numbers to show how this improves
    > things? I read the patches, but I'm not strong enough to comment on
    > them at all. But I am interested in how this improves writeback under
    > pressure, if at all.

    Writeback should be about the same, it's mostly about preventing
    softlockups and excessive memory usage, under conditions where we are
    actively trying to reclaim/clean memory. It was bad enough to cause
    softlockups for writeback work processing, while the pending writeback
    work units grew to insane lengths.

    --
    Jens Axboe

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