On Tue, Feb 12, 2019 at 5:38 PM Raghavendra Gowdappa <[email protected]> wrote:
> All, > > We've found perf xlators io-cache and read-ahead not adding any > performance improvement. At best read-ahead is redundant due to kernel > read-ahead > One thing we are still figuring out is whether kernel read-ahead is tunable. From what we've explored, it _looks_ like (may not be entirely correct), ra is capped at 128KB. If that's the case, I am interested in few things: * Are there any realworld applications/usecases, which would benefit from larger read-ahead (Manoj says block devices can do ra of 4MB)? * Is the limit on kernel ra tunable a hard one? IOW, what does it take to make it to do higher ra? If its difficult, can glusterfs read-ahead provide the expected performance improvement for these applications that would benefit from aggressive ra (as glusterfs can support larger ra sizes)? I am still inclined to prefer kernel ra as I think its more intelligent and can identify more sequential patterns than Glusterfs read-ahead [1][2]. [1] https://www.kernel.org/doc/ols/2007/ols2007v2-pages-273-284.pdf [2] https://lwn.net/Articles/155510/ and at worst io-cache is degrading the performance for workloads that > doesn't involve re-read. Given that VFS already have both these > functionalities, I am proposing to have these two translators turned off by > default for native fuse mounts. > > For non-native fuse mounts like gfapi (NFS-ganesha/samba) we can have > these xlators on by having custom profiles. Comments? > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1665029 > > regards, > Raghavendra >
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