Hi, On Fri 21-05-10 08:48:57, KOSAKI Motohiro wrote: > CC to Nick and Jan Thanks. > > We've seen multiple performance regressions linked to the lower(20%) > > dirty_ratio. When performing enough IO to overwhelm the background > > flush daemons the percent of dirty pagecache memory quickly climbs > > to the new/lower dirty_ratio value of 20%. At that point all writing > > processes are forced to stop and write dirty pagecache pages back to disk. > > This causes performance regressions in several benchmarks as well as causing > > a noticeable overall sluggishness. We all know that the dirty_ratio is > > an integrity vs performance trade-off but the file system journaling > > will cover any devastating effects in the event of a system crash. > > > > Increasing the dirty_ratio to 40% will regain the performance loss seen > > in several benchmarks. Whats everyone think about this??? > > In past, Jan Kara also claim the exactly same thing. > > Subject: [LSF/VM TOPIC] Dynamic sizing of dirty_limit > Date: Wed, 24 Feb 2010 15:34:42 +0100 > > > (*) 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. > > So, I'd prefer to restore the default rather than both Redhat and SUSE apply exactly > same distro specific patch. because we can easily imazine other users will face the same > issue in the future. > > Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > Nick, Jan, if the above is too old and your distro have been dropped the patch, please > correct me. No, SLE11 SP1 still has a patch that increases dirty_ratio to 40. But on the other hand I agree with Zan that for desktop, 40% of memory for dirty data is a lot these days and takes a long time to write out (it could easily be 30s - 1m). On a desktop the memory is much better used as a read-only pagecache or for memory hungry apps like Firefox or Acrobat Reader. So I believe for a desktop the current setting (20) is a better choice. So until we find a way how to dynamically size the dirty limit, we have to decide whether we want to have a default setting for a server or for a desktop... Personally, I don't care very much and I feel my time would be better spent thinking about dynamic limit sizing rather than arguing what is better default ;). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>