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Groups > linux.kernel > #1362938

Re: [PATCH 6/6] writeback: throttle buffered writeback

From Jens Axboe <axboe@fb.com>
Newsgroups linux.kernel
Subject Re: [PATCH 6/6] writeback: throttle buffered writeback
Date 2016-03-22 21:20 +0100
Message-ID <rfAWt-1e6-1@gated-at.bofh.it> (permalink)
References <rfyKZ-88A-3@gated-at.bofh.it> <rfyL0-88A-19@gated-at.bofh.it> <rfAWt-1e6-3@gated-at.bofh.it>
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On 03/22/2016 02:12 PM, Jeff Moyer wrote:
> Hi, Jens,
>
> Jens Axboe <axboe@fb.com> writes:
>
>> If the device has write back caching, 'wb_cache_delay' delays by
>> this amount of usecs when a write completes before allowing more.
>
> What's the reason behind that?

For classic write back caching, the cache can absorb a bunch of writes 
shortly, which means that the completion cost only shows a small part of 
the overall cost. This means that if we just throttle on completion, 
then when the device starts committing to media, then we'll end up 
starving other IO anyway. This knob is a way to attempt to tame that.

-- 
Jens Axboe

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Thread

[PATCH 6/6] writeback: throttle buffered writeback Jens Axboe <axboe@fb.com> - 2016-03-22 19:00 +0100
  Re: [PATCH 6/6] writeback: throttle buffered writeback Jens Axboe <axboe@fb.com> - 2016-03-22 21:20 +0100
    Re: [PATCH 6/6] writeback: throttle buffered writeback Jeff Moyer <jmoyer@redhat.com> - 2016-03-22 21:30 +0100
    Re: [PATCH 6/6] writeback: throttle buffered writeback Jens Axboe <axboe@fb.com> - 2016-03-22 22:40 +0100
    Re: [PATCH 6/6] writeback: throttle buffered writeback Shaohua Li <shli@kernel.org> - 2016-03-22 22:40 +0100
  Re: [PATCH 6/6] writeback: throttle buffered writeback Jeff Moyer <jmoyer@redhat.com> - 2016-03-22 21:20 +0100

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