Re: [PATCH 6/6] writeback: throttle buffered writeback
From: Jens Axboe
Date: Tue Mar 22 2016 - 16:19:43 EST
On 03/22/2016 02:12 PM, Jeff Moyer wrote:
Jens Axboe <axboe@xxxxxx> 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.