On Wed, 18 May 2016, Jianjian Huo wrote: > On Wed, May 18, 2016 at 10:19 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote: > > > > Hi Rajath! > > > > Great to hear you're interested in working with us outside of GSoC! > > > > On Wed, 18 May 2016, Haomai Wang wrote: > > > Hi Rajath, > > > > > > We are glad to see your passion, from my view, sage is planning to > > > implement a userspace cache in bluestore itself. Like > > > (https://github.com/ceph/ceph/commit/b9ac31afe5a162176f019baa25348014a77f6ab8#commitcomment-17488250). > > > > > > I guess the cache won't be a generic cache interface. Instead it will > > > be bound to specified needed object. So sage may give a brief? > > > > Part of the reason why this project wasn't at the top of our list (we got > > fewer slots than we had projects) was because the BlueStore code is in > > flux and moving quite quickly. For the BlueStore side, we are building a > > simple buffer cache that is tied to an Onode (in-memory per-object > > metadata structure) and integrated tightly with the read and write IO > > paths. This will eliminate our use of the block device buffer cache for > > user/object data. > > > > The other half of the picture, though, is the BlueFS layer that is > > consumed by rocksdb: it also needs caching in order for rocksdb to perform > > at all. My hope is that the code we write for the use data can be re-used > > here as well, but it is still evolving. > > When Bluestore moves away from kernel cache to its own buffer cache, RocksDB can use its own buffer cache as well. > RocksDB has this size configurable block cache to cache uncompressed data blocks, it can serve as buffer cache, > since Bluestore don't compress meta data in RocksDB. What options control this? I was having trouble finding it the last time I looked. We should switch it now (and use unbuffered IO from BlueFS) if we can. Thanks! sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
