On Fri, Feb 23, 2007 at 09:25:28AM -0800, Zach Brown wrote: > > On Feb 23, 2007, at 7:37 AM, Nick Piggin wrote: > > > > >The dentry hash uses up 8MB for 1 million entries on my 4GB system > >is one > >of the biggest wasters of memory for me. Because I rarely have more > >than one or > >two hundred thousand dentries. And that's with several kernel trees > >worth of > >entries. Most desktop and probably even many types of servers will > >only use a > >fraction of that. > > > >So I introduce a new method for resizing hash tables with RCU, and > >apply > >that to the dentry hash. > > Can you compare what you've done to the design that Paul and David > talked about a year ago? > > http://lkml.org/lkml/2006/1/30/74
Thanks for the link, I wasn't aware of Paul's algorithm before. I guess most variants are going to have a double pointer scheme, so they are similar in that regard. I think Paul's is quite complex in moving entries to the new table, and it looks like it requires a lot of grace periods. I avoid all that by using the seqlock. It wasn't clear to me how Paul handled the case where an item is present in the not_current table, but the lookup misses it when it gets moved between the tables. It is a little tricky to follow the find details because it is not in code or pseudo code format. > I'd love to see a generic implementation of RCU hashing that > subsystems can then take advantage of. It's long been on the fun > side of my todo list. The side I never get to :/. Yeah if this is to be used anywhere else, I think it definitely needs to be made into a generic library if possible. Main thing I wanted was to get something working and see what people think about it. Thanks, Nick - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/