On Wed, May 18, 2016 at 6:35 PM, Haomai Wang <haomai@xxxxxxxx> wrote: > On Thu, May 19, 2016 at 7:50 AM, Jianjian Huo <jianjian.huo@xxxxxxxxxxx> 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. > > Actually this is not behaviored as expected. From my last nvmedevice > benchmark, lots of read still go down device instead of caching by > rocksdb when I set a very large block cache. I guess there exists some > gaps between our usages and rocksdb implementation What kind of workload did you use for that benchmarking, 100% read? > >> >> Jianjian >>> >>> The main missing piece I'd say is a way to string Buffer objects together >>> in a global(ish) LRU (or set of LRUs, or whatever we need for the caching >>> policy that makes sense) so that trimming can be done safely and >>> efficiently. Right now the code is lock-free because each Onode is only >>> touched under the collection rwlock, but in order to do trimming we need >>> to be able to reap cold buffers from a global context. >>> >>> Anyway, there is no clear or ready answer here yet, but we are ready to >>> discuss design/approach here on the list, and welcome your input (and >>> potentially, contributions to development!). >>> >>> sage >>> >>> >>> > >>> > On Wed, May 18, 2016 at 9:32 PM, Haomai Wang <haomai@xxxxxxxx> wrote: >>> > > >>> > > >>> > > On Wed, May 18, 2016 at 2:44 PM, Rajath Shashidhara >>> > > <rajath.shashidhara@xxxxxxxxx> wrote: >>> > >> >>> > >> Hello, >>> > >> >>> > >> I was a GSoC'16 applicant for the project "Implementing Cache layer on >>> > >> top of NVME Driver". Unfortunately, I was not selected for the >>> > >> internship. >>> > > >>> > > >>> > > 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? >>> > > >>> > >> >>> > >> >>> > >> However, I would be interested in working on the project as an >>> > >> independent contributor to Ceph. >>> > >> I am expecting to receive the necessary support from Ceph developer >>> > >> community. >>> > >> >>> > >> In case I missed out any important details in my project proposal or I >>> > >> have the wrong understanding of the project, please help me figure out >>> > >> the details. >>> > >> >>> > >> Looking forward to contribute! >>> > >> >>> > >> Thank you, >>> > >> Rajath Shashidhara >>> > > >>> > > >>> > -- >>> > 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 >>> > >>> > >>> -- >>> 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 > -- > 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 ��.n��������+%������w��{.n����z��u���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
