On 2017/9/27 上午3:24, Michael Lyle wrote: > This works in conjunction with the new PI controller. Currently, in > real-world workloads, the rate controller attempts to write back 1 > sector per second. In practice, these minimum-rate writebacks are > between 4k and 60k in test scenarios, since bcache aggregates and > attempts to do contiguous writes and because filesystems on top of > bcachefs typically write 4k or more. > > Previously, bcache used to guarantee to write at least once per second. > This means that the actual writeback rate would exceed the configured > amount by a factor of 8-120 or more. > > This patch adjusts to be willing to sleep up to 2.5 seconds, and to > target writing 4k/second. On the smallest writes, it will sleep 1 > second like before, but many times it will sleep longer and load the > backing device less. This keeps the loading on the cache and backing > device related to writeback more consistent when writing back at low > rates. > > Signed-off-by: Michael Lyle <mlyle@xxxxxxxx> Reviewed-by: Coly Li <colyli@xxxxxxx> Added to for-test. Thanks. > --- > drivers/md/bcache/util.c | 10 ++++++++-- > drivers/md/bcache/writeback.c | 2 +- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c > index 176d3c2ef5f5..4dbe37e82877 100644 > --- a/drivers/md/bcache/util.c > +++ b/drivers/md/bcache/util.c > @@ -232,8 +232,14 @@ uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done) > > d->next += div_u64(done * NSEC_PER_SEC, d->rate); > > - if (time_before64(now + NSEC_PER_SEC, d->next)) > - d->next = now + NSEC_PER_SEC; > + /* Bound the time. Don't let us fall further than 2 seconds behind > + * (this prevents unnecessary backlog that would make it impossible > + * to catch up). If we're ahead of the desired writeback rate, > + * don't let us sleep more than 2.5 seconds (so we can notice/respond > + * if the control system tells us to speed up!). > + */ > + if (time_before64(now + NSEC_PER_SEC * 5 / 2, d->next)) > + d->next = now + NSEC_PER_SEC * 5 / 2; > > if (time_after64(now - NSEC_PER_SEC * 2, d->next)) > d->next = now - NSEC_PER_SEC * 2; > diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c > index 5a8f5655151b..0b7c89813635 100644 > --- a/drivers/md/bcache/writeback.c > +++ b/drivers/md/bcache/writeback.c > @@ -523,7 +523,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc) > dc->writeback_percent = 10; > dc->writeback_delay = 30; > dc->writeback_rate.rate = 1024; > - dc->writeback_rate_minimum = 1; > + dc->writeback_rate_minimum = 8; > > dc->writeback_rate_update_seconds = 5; > dc->writeback_rate_p_term_inverse = 40; > -- Coly Li -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
