>From https://bugzilla.lustre.org/show_bug.cgi?id=22771#c24 : > On our production system, the hash table contain 64 entries (6 bits) for a > cache of 2307267 entries. > A count in each list give a good load balance : number of entries vary > between 35782 to 36496 while the optimal repartition is 2307267 / 64 = > 36051. Hehe, I like that sense of humor :) On Thursday 22 July 2010 01:18:39 Andreas Dilger wrote: > Is it possible to allow mbcache to be disabled, either for the whole > kernel, on a per-filesystem basis, or adaptively if the cache hit rate is > very low (any of these is fine, not all of them). We could do that, but making the cache not degrade so badly would be a good idea in any case. The number of buckets is currently fixed for ext[234] so it would make sense to either make that number dynamic or limit the maximum number of cache entries. The latter will probably be good enough for most workloads. > Attached is a patch that allows manually disabling mbcache on a > per-filesystem basis with a mount option. > I don't think fixing the mbcache to be more efficient (more buckets, more > locks, etc) is really solving the problem which is that mbcache is adding > overhead without value in these situations. A mount option would be very ugly, but a kernel internal NO_MBCACHE flag sounds more acceptable to me. > Better would be to > automatically disable it if e.g. some hundreds or thousands of objects > were inserted into the cache and there was < 1% cache hit rate. This assumes that the workload won't change. > That would help everyone, even those people who don't know they have a > problem. People who don't know they have a problem would also be helped by making the cache not degrade so badly, right? Even better would be to use a more appropriate inode size, but you've pointed that out in the bug already. Thanks, Andreas -- 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
