On Thu, Mar 3, 2016 at 3:11 AM, Rajath Shashidhara <rajath.shashidhara@xxxxxxxxx> wrote: > I did some reading on user space drivers and specifically NVME drivers > [1,2]. I understand that user space drivers run in "user mode" as > opposed to the "kernel mode" to save context switch time. But, this > also places several restrictions on the driver, like the > unavailability of buffer cache usually present to optimize read/write > from storage devices in the kernel. > > I would like to know more about the following things to understand the > cache requirements : > [1] Are there any assumptions that I should make about locality of access ? Yep, I think you should know about bluestore arch firstly. This slide(http://www.slideshare.net/sageweil1/ceph-and-rocksdb?qid=3021e4f1-58b5-4758-aa64-7005e3b98f51&v=&b=&from_search=7) is great to know. I think if we can separate data and metadata cache, it would be better(just a idea). The metadata workload is very critical for cache design and implementation, so you can give a look at details about how rocksdb access BlockDevice. This part contains rocksdb itself and RocksDBEnv at ceph side. About data part, I think it should be generic. > [2] Are multiple threads going to be accessing the cache at the same > time (thread safety) ? Yes or not, you can implement a shared cache which accessed by multi threads, or you can build a local cache which owned by only a thread. I think a suitable design match bluestore is the best. > [3] What are the components in Ceph that are going to directly > interact with the cache ? (Reading their code might give me a better > idea about what is expected of me) >From current status, I think we only need to focus on bluestore part. > > When designing a cache there are several parameters/factors that needs > to be addresses - like page replacement policies, page sizes, > prefetching, etc. I guess I will be able to make the right design > choices if I better understand the cache requirements and access > profile. > > This is my first exposure to ceph. Please excuse me if I am asking > basic questions. > > Please point me to the right resources so that I can better understand > the project. I would also be happy to fix a bug to familiarize myself > with the source code. Any suggestions on bugs that are relevant to the > project will be of great help. > > Thank you, > Rajath Shashidhara > > [1] http://www.enea.com/Documents/Resources/Whitepapers/Enea-User-Space-Drivers-in-Linux_Whitepaper_2013.pdf > [2] http://www.nvmexpress.org/about/nvm-express-overview/ > > On Wed, Mar 2, 2016 at 5:57 AM, Josh Durgin <jdurgin@xxxxxxxxxx> wrote: >> On 03/01/2016 06:01 AM, Haomai Wang wrote: >>> >>> I think it's a initial idea background, but since we also have >>> ObjectCacher in client side, if we can unify this it will be good. But >>> obviously ObjectCacher is complexity now, you may not take care of it >>> at first... >> >> >> I'd suggest ignoring ObjectCacher, since it's got ordering and buffer >> assumptions you probably don't need, plus a single global lock. I'd >> expect a read-focused cache to be pretty different. >> >> Josh > -- > 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
