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Re: [PATCH 0/12 v3] Writeback improvements

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On Wed, Sep 27, 2017 at 02:13:47PM -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 for that issue is patch 10. The rest are cleanups,
> as well as the removal of doing non-range cyclic writeback. The users
> of that was sync_inodes_sb() and wakeup_flusher_threads(), both of
> which writeback all of the dirty pages.

So does this patch set make things faster?  Less bursty?  Does it make
writeout take longer, but with less spikes?  What is the performance
impact of this change?   I hate to be a pain, but this just smacks of
arm waving and I'm sure FB doesn't make changes without data... :-)

> 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.

Do you push back on the callers or slow them down?  Why do we even
allow callers to flush everything?

John

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[PATCH 0/12 v3] Writeback improvements Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 10/12] writeback: only allow one inflight and pending full flush Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
    Re: [PATCH 10/12] writeback: only allow one inflight and pending  full flush Andrew Morton <akpm@linux-foundation.org> - 2017-09-28 23:50 +0200
      Re: [PATCH 10/12] writeback: only allow one inflight and pending full flush Linus Torvalds <torvalds@linux-foundation.org> - 2017-09-28 23:50 +0200
        Re: [PATCH 10/12] writeback: only allow one inflight and pending full  flush Jens Axboe <axboe@kernel.dk> - 2017-09-29 02:20 +0200
          Re: [PATCH 10/12] writeback: only allow one inflight and pending full flush Amir Goldstein <amir73il@gmail.com> - 2017-09-29 07:30 +0200
      Re: [PATCH 10/12] writeback: only allow one inflight and pending full  flush Jens Axboe <axboe@kernel.dk> - 2017-09-29 02:20 +0200
  [PATCH 04/12] fs: kill 'nr_pages' argument from wakeup_flusher_threads() Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 09/12] writeback: move nr_pages == 0 logic to one location Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 01/12] buffer: have alloc_page_buffers() use __GFP_NOFAIL Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
    Re: [PATCH 01/12] buffer: have alloc_page_buffers() use __GFP_NOFAIL Nikolay Borisov <nborisov@suse.com> - 2017-09-28 17:30 +0200
  [PATCH 03/12] buffer: eliminate the need to call free_more_memory() in __getblk_slow() Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
    Re: [PATCH 03/12] buffer: eliminate the need to call  free_more_memory() in __getblk_slow() Nikolay Borisov <nborisov@suse.com> - 2017-09-28 17:40 +0200
  [PATCH 06/12] writeback: provide a wakeup_flusher_threads_bdi() Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 05/12] writeback: switch wakeup_flusher_threads() to cyclic writeback Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 11/12] writeback: make sync_inodes_sb() use range cyclic writeback Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  [PATCH 07/12] writeback: pass in '0' for nr_pages writeback in laptop mode Jens Axboe <axboe@kernel.dk> - 2017-09-27 22:20 +0200
  Re: [PATCH 0/12 v3] Writeback improvements John Stoffel <john@quad.stoffel.home> - 2017-09-28 15:20 +0200
    Re: [PATCH 0/12 v3] Writeback improvements Jens Axboe <axboe@kernel.dk> - 2017-09-28 15:50 +0200

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