Hi, one more suggestion for discussion: Currently, the amount of dirtiable memory is fixed - either to a percentage of ram (dirty_limit) or to a fix number of megabytes. The problem with this is that if you have application doing random writes on a file (like some simple databases do), you'll get a big performance improvement if you increase the amount of dirtiable memory (because you safe quite some rewrites and also get larger chunks of sequential IO) (*) On the other hand for sequential IO increasing dirtiable memory (beyond certain level) does not really help - you end up doing the same IO. So for a machine is doing sequential IO, having 10% of memory dirtiable is just fine (and you probably don't want much more because the memory is better used for something else), when a machine does random rewrites, going to 40% might be well worth it. So I'd like to discuss how we could measure that increasing amount of dirtiable memory helps so that we could implement dynamic sizing of it. (*) We ended up increasing dirty_limit in SLES 11 to 40% as it used to be with old kernels because customers running e.g. LDAP (using BerkelyDB heavily) were complaining about performance problems. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
