Skip to content

L
linux
Switch branch/tag
  1. 10 Feb, 2021 4 commits
    • Kai Krakow's avatar
      bcache: Give btree_io_wq correct semantics again · d797bd98
      Kai Krakow authored 
      Before killing `btree_io_wq`, the queue was allocated using
`create_singlethread_workqueue()` which has `WQ_MEM_RECLAIM`. After
killing it, it no longer had this property but `system_wq` is not
single threaded.

Let's combine both worlds and make it multi threaded but able to
reclaim memory.

Cc: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: default avatarKai Krakow <kai@kaishome.de>
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      d797bd98
    • Kai Krakow's avatar
      Revert "bcache: Kill btree_io_wq" · 9f233ffe
      Kai Krakow authored 
      This reverts commit 56b30770.

With the btree using the `system_wq`, I seem to see a lot more desktop
latency than I should.

After some more investigation, it looks like the original assumption
of 56b30770 no longer is true, and bcache has a very high potential of
congesting the `system_wq`. In turn, this introduces laggy desktop
performance, IO stalls (at least with btrfs), and input events may be
delayed.

So let's revert this. It's important to note that the semantics of
using `system_wq` previously mean that `btree_io_wq` should be created
before and destroyed after other bcache wqs to keep the same
assumptions.

Cc: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: default avatarKai Krakow <kai@kaishome.de>
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      9f233ffe
    • Kai Krakow's avatar
      bcache: Fix register_device_aync typo · d7fae7b4
      Kai Krakow authored 
      Should be `register_device_async`.

Cc: Coly Li <colyli@suse.de>
Signed-off-by: default avatarKai Krakow <kai@kaishome.de>
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      d7fae7b4
    • dongdong tao's avatar
      bcache: consider the fragmentation when update the writeback rate · 71dda2a5
      dongdong tao authored 
      Current way to calculate the writeback rate only considered the
dirty sectors, this usually works fine when the fragmentation
is not high, but it will give us unreasonable small rate when
we are under a situation that very few dirty sectors consumed
a lot dirty buckets. In some case, the dirty bucekts can reached
to CUTOFF_WRITEBACK_SYNC while the dirty data(sectors) not even
reached the writeback_percent, the writeback rate will still
be the minimum value (4k), thus it will cause all the writes to be
stucked in a non-writeback mode because of the slow writeback.

We accelerate the rate in 3 stages with different aggressiveness,
the first stage starts when dirty buckets percent reach above
BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW (50), the second is
BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID (57), the third is
BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH (64). By default
the first stage tries to writeback the amount of dirty data
in one bucket (on average) in (1 / (dirty_buckets_percent - 50)) second,
the second stage tries to writeback the amount of dirty data in one bucket
in (1 / (dirty_buckets_percent - 57)) * 100 millisecond, the third
stage tries to writeback the amount of dirty data in one bucket in
(1 / (dirty_buckets_percent - 64)) millisecond.

the initial rate at each stage can be controlled by 3 configurable
parameters writeback_rate_fp_term_{low|mid|high}, they are by default
1, 10, 1000, the hint of IO throughput that these values are trying
to achieve is described by above paragraph, the reason that
I choose those value as default is based on the testing and the
production data, below is some details:

A. When it comes to the low stage, there is still a bit far from the 70
   threshold, so we only want to give it a little bit push by setting the
   term to 1, it means the initial rate will be 170 if the fragment is 6,
   it is calculated by bucket_size/fragment, this rate is very small,
   but still much reasonable than the minimum 8.
   For a production bcache with unheavy workload, if the cache device
   is bigger than 1 TB, it may take hours to consume 1% buckets,
   so it is very possible to reclaim enough dirty buckets in this stage,
   thus to avoid entering the next stage.

B. If the dirty buckets ratio didn't turn around during the first stage,
   it comes to the mid stage, then it is necessary for mid stage
   to be more aggressive than low stage, so i choose the initial rate
   to be 10 times more than low stage, that means 1700 as the initial
   rate if the fragment is 6. This is some normal rate
   we usually see for a normal workload when writeback happens
   because of writeback_percent.

C. If the dirty buckets ratio didn't turn around during the low and mid
   stages, it comes to the third stage, and it is the last chance that
   we can turn around to avoid the horrible cutoff writeback sync issue,
   then we choose 100 times more aggressive than the mid stage, that
   means 170000 as the initial rate if the fragment is 6. This is also
   inferred from a production bcache, I've got one week's writeback rate
   data from a production bcache which has quite heavy workloads,
   again, the writeback is triggered by the writeback percent,
   the highest rate area is around 100000 to 240000, so I believe this
   kind aggressiveness at this stage is reasonable for production.
   And it should be mostly enough because the hint is trying to reclaim
   1000 bucket per second, and from that heavy production env,
   it is consuming 50 bucket per second on average in one week's data.

Option writeback_consider_fragment is to control whether we want
this feature to be on or off, it's on by default.

Lastly, below is the performance data for all the testing result,
including the data from production env:
https://docs.google.com/document/d/1AmbIEa_2MhB9bqhC3rfga9tp7n9YX9PLn0jSUxscVW0/edit?usp=sharingSigned-off-by: default avatardongdong tao <dongdong.tao@canonical.com>
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      71dda2a5
  3. 04 Feb, 2021 5 commits
  5. 02 Feb, 2021 23 commits
  7. 31 Jan, 2021 1 commit
  9. 26 Jan, 2021 7 commits
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7