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 > Looks like it's a bit harder to disable mbcache than I thought. I ended up adding code to collect the statics. With selinux enabled, for new_fserver workload of aim7, there are a total of 0x7e05420100000000 ext4_xattr_cache_find() calls that result in a hit and 0xc100000000000000 calls that are not. The number does not seem to favor the complete disabling of mbcache in this case. Thanks, Mak. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
