Hey - set cache_mode to writethrough, and then if you really want everything to hit the cache, also set both congested_thresholds to 0 On Sat, Nov 3, 2012 at 11:53 AM, James Sefton <james@xxxxxxxxxxxx> wrote: > Hi Kent, > > I am trying to configure the cache to always cache. > The only time I want it to bypass the cache is when it has to. (ie.. cache > full) > > In particular - I want all writes to hit the writeback cache and never be > written directly. (Unless no space is left for writeback) > > I am not sure how to configure this. I thought I had done it once before but I > cant seem to reproduce it. > > Here are my settings so far: > > /sys/block/bcache0/bcache/ > > cache_mode = writethrough [writeback] writearound none > readahead = 0 > running = 1 > sequential_cutoff = 0 (also tried this at 1.1G, which appears to be maximum) > sequential_merge = 1 (also tried 0. I have no idea what this means) > state = clean > writeback_delay = 30 > writeback_metadata = 1 (not sure what this does) > writeback_percent = 40 (also tried at 10) > writeback_running = 1 > > > not sure what else there is to configure. > Any suggestions would be appreciated. > > I am basically trying to maintain responsive disk access as much as possible. > The backing storage is on a slow link to a SAN and when accessed directly is > relatively slow. I want it to use the cache as much as is possible and then > bCache write the cache data to the backend storage behind the scenes. Workload > is mixed.. random and sequential reads and writes, anything from just a few > bytes to 4-5Gb files. > > I am guessing that sequential_cutoff = 0 disables the cut-off feature. (I tried > the max of 1.1G too, just in case) > > I am using nmon to monitor where data is being written while copying /usr into > the filesystem on cache0p1. (ext4) I am seeing writes going to the cache > device and the backing device simultaneously - but the cache is not written to > heavily. Performance seen when copying is similar to that of if I was just > writing to the backing device directly. (maybe a little better since some bits > are getting written to the cache) > > Any suggestion what I may be doing wrong? > > Cheers, > > James > > -- > To unsubscribe from this list: send the line "unsubscribe linux-bcache" 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 linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
