kernel.git/drivers/md/bcache/bcache.h, branch linux-5.14.y

bcache: remove bcache device self-defined readahead

2021-06-08T21:06:03Z

For read cache missing, bcache defines a readahead size for the read I/O request to the backing device for the missing data. This readahead size is initialized to 0, and almost no one uses it to avoid unnecessary read amplifying onto backing device and write amplifying onto cache device. Considering upper layer file system code has readahead logic allready and works fine with readahead_cache_policy sysfile interface, we don't have to keep bcache self-defined readahead anymore. This patch removes the bcache self-defined readahead for cache missing request for backing device, and the readahead sysfs file interfaces are removed as well. This is the preparation for next patch to fix potential kernel panic due to oversized request in a simpler method. Reported-by: Alexander Ullrich Reported-by: Diego Ercolani Reported-by: Jan Szubiak Reported-by: Marco Rebhan Reported-by: Matthias Ferdinand Reported-by: Victor Westerhuis Reported-by: Vojtech Pavlik Reported-and-tested-by: Rolf Fokkens Reported-and-tested-by: Thorsten Knabe Signed-off-by: Coly Li Reviewed-by: Christoph Hellwig Cc: stable@vger.kernel.org Cc: Kent Overstreet Cc: Nix Cc: Takashi Iwai Link: https://lore.kernel.org/r/20210607125052.21277-2-colyli@suse.de Signed-off-by: Jens Axboe

bcache: remove PTR_CACHE

2021-04-11T14:37:55Z

Remove the PTR_CACHE inline and replace it with a direct dereference of c->cache. (Coly Li: fix the typo from PTR_BUCKET to PTR_CACHE in commit log) Signed-off-by: Christoph Hellwig Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20210411134316.80274-3-colyli@suse.de Signed-off-by: Jens Axboe

bcache: Move journal work to new flush wq

2021-02-10T15:06:00Z

This is potentially long running and not latency sensitive, let's get it out of the way of other latency sensitive events. As observed in the previous commit, the `system_wq` comes easily congested by bcache, and this fixes a few more stalls I was observing every once in a while. Let's not make this `WQ_MEM_RECLAIM` as it showed to reduce performance of boot and file system operations in my tests. Also, without `WQ_MEM_RECLAIM`, I no longer see desktop stalls. This matches the previous behavior as `system_wq` also does no memory reclaim: > // workqueue.c: > system_wq = alloc_workqueue("events", 0, 0); Cc: Coly Li Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Kai Krakow Signed-off-by: Coly Li Signed-off-by: Jens Axboe

Revert "bcache: Kill btree_io_wq"

2021-02-10T15:06:00Z

This reverts commit 56b30770b27d54d68ad51eccc6d888282b568cee. 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 56b3077 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 Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Kai Krakow Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: consider the fragmentation when update the writeback rate

2021-02-10T15:05:59Z

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=sharing Signed-off-by: dongdong tao Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: remove embedded struct cache_sb from struct cache_set

2020-10-02T20:25:30Z

Since bcache code was merged into mainline kerrnel, each cache set only as one single cache in it. The multiple caches framework is here but the code is far from completed. Considering the multiple copies of cached data can also be stored on e.g. md raid1 devices, it is unnecessary to support multiple caches in one cache set indeed. The previous preparation patches fix the dependencies of explicitly making a cache set only have single cache. Now we don't have to maintain an embedded partial super block in struct cache_set, the in-memory super block can be directly referenced from struct cache. This patch removes the embedded struct cache_sb from struct cache_set, and fixes all locations where the superb lock was referenced from this removed super block by referencing the in-memory super block of struct cache. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: only use bucket_bytes() on struct cache

2020-10-02T20:25:30Z

Because struct cache_set and struct cache both have struct cache_sb, macro bucket_bytes() currently are used on both of them. When removing the embedded struct cache_sb from struct cache_set, this macro won't be used on struct cache_set anymore. This patch unifies all bucket_bytes() usage only on struct cache, this is one of the preparation to remove the embedded struct cache_sb from struct cache_set. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: remove useless bucket_pages()

2020-10-02T20:25:30Z

It seems alloc_bucket_pages() is the only user of bucket_pages(). Considering alloc_bucket_pages() is removed from bcache code, it is safe to remove the useless macro bucket_pages() now. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: only use block_bytes() on struct cache

2020-10-02T20:25:30Z

Because struct cache_set and struct cache both have struct cache_sb, therefore macro block_bytes() can be used on both of them. When removing the embedded struct cache_sb from struct cache_set, this macro won't be used on struct cache_set anymore. This patch unifies all block_bytes() usage only on struct cache, this is one of the preparation to remove the embedded struct cache_sb from struct cache_set. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: add set_uuid in struct cache_set

2020-10-02T20:25:30Z

This patch adds a separated set_uuid[16] in struct cache_set, to store the uuid of the cache set. This is the preparation to remove the embedded struct cache_sb from struct cache_set. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe