Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 6/6] writeback: throttle buffered writeback | Date | Tue, 22 Mar 2016 16:27:29 -0400 |
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Jens Axboe <axboe@fb.com> writes:
> 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.
Ah, makes perfect sense. Thanks!
-Jeff
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