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Re: [PATCHSET v3][RFC] Make background writeback not suck

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On Thu, Mar 31, 2016 at 10:09:56PM +0000, Holger Hoffstätte wrote:
> 
> Hi,
> 
> Jens mentioned on Twitter I should post my experience here as well,
> so here we go.
> 
> I've backported this series (incl. updates) to stable-4.4.x - not too
> difficult, minus the NVM part which I don't need anyway - and have been
> running it for the past few days without any problem whatsoever, with
> GREAT success.
> 
> My use case is primarily larger amounts of stuff (transcoded movies,
> finished downloads, built Gentoo packages) that gets copied from tmpfs
> to SSD (or disk) and every time that happens, the system noticeably
> strangles readers (desktop, interactive shell). It does not really matter
> how I tune writeback via the write_expire/dirty_bytes knobs or the
> scheduler (and yes, I understand how they work); lowering the writeback
> limits helped a bit but the system is still overwhelmed. Jacking up
> deadline's writes_starved to unreasonable levels helps a bit, but in turn
> makes all writes suffer. Anything else - even tried BFQ for a while,
> which has its own unrelated problems - didn't really help either.

Can you go back to your original kernel, and lower nr_requests to 8?

Essentially all I see the block throttle doing is keeping the
request queue depth to somewhere between 8-12 requests, rather than
letting it blow out to near nr_requests (around 105-115), so it
would be interesting to note whether the block throttling has any
noticable difference in behaviour when compared to just having a
very shallow request queue....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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[PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-03-30 17:20 +0200
  [PATCH 3/9] writeback: use WRITE_SYNC for reclaim or sync writeback Jens Axboe <axboe@fb.com> - 2016-03-30 17:20 +0200
  [PATCH 6/9] sd: inform block layer of write cache state Jens Axboe <axboe@fb.com> - 2016-03-30 17:20 +0200
  Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-03-31 10:30 +0200
    Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-03-31 16:30 +0200
      Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-03-31 18:30 +0200
        Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 03:00 +0200
          Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 05:30 +0200
            Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 05:40 +0200
            Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 05:40 +0200
              Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 08:20 +0200
                Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 16:40 +0200
            Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 07:10 +0200
      Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 02:50 +0200
        Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 05:30 +0200
          Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 08:30 +0200
            Re: [PATCHSET v3][RFC] Make background writeback not suck Jens Axboe <axboe@fb.com> - 2016-04-01 16:40 +0200
  Re: [PATCHSET v3][RFC] Make background writeback not suck Holger Hoffstätte   <holger.hoffstaette@googlemail.com> - 2016-04-01 00:20 +0200
    Re: [PATCHSET v3][RFC] Make background writeback not suck Dave Chinner <david@fromorbit.com> - 2016-04-01 03:10 +0200
      Re: [PATCHSET v3][RFC] Make background writeback not suck Holger Hoffstätte   <holger.hoffstaette@googlemail.com> - 2016-04-01 19:10 +0200

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