On 09/04/2013 08:00 PM, Andreas Dilger wrote: > > In the past, I've raised the question of whether mbcache is even > useful on real-world systems. Essentially, this is providing a > "deduplication" service for ext2/3/4 xattr blocks that are identical. > The question is how often this is actually the case in modern use? > The original design was for allowing external ACL blocks to be > shared between inodes, at a time when ACLs where pretty much the > only xattrs stored on inodes. > > The question now is whether there are common uses where all of the > xattrs stored on multiple inodes are identical? If that is not the > case, mbcache is just adding overhead and should just be disabled > entirely instead of just adding less overhead. > > There aren't good statistics on the hit rate for mbcache, but it > might be possible to generate some with systemtap or similar to > see how often ext4_xattr_cache_find() returns NULL vs. non-NULL. > > Cheers, Andreas > Thanks Andreas for the comments. Since I'm not familiar with systemtap, I'm thinking probably the quickest and simplest way is to re-run aim7 and swing bench with mbcache disabled for comparison. Please let me know if you have any other benchmark suggestion or if you think systemtap on ext4_xattr_cache_find() would give a more accurate measurement. Thanks, Mak. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
