Sasha Levin <levinsasha928@xxxxxxxxx> writes: > On 08/15/2012 03:08 AM, Eric W. Biederman wrote: >>> I can offer the following: I'll write a small module that will hash 1...10000 >>> > into a hashtable which uses 7 bits (just like user_ns) and post the distribution >>> > we'll get. >> That won't hurt. I think 1-100 then 1000-1100 may actually be more >> representative. Not that I would mind seeing the larger range. >> Especially since I am in the process of encouraging the use of more >> uids. >> > > Alrighty, the results are in (numbers are objects in bucket): > > For the 0...10000 range: > > Average: 78.125 > Std dev: 1.4197704151 > Min: 75 > Max: 80 > > > For the 1...100 range: > > Average: 0.78125 > Std dev: 0.5164613088 > Min: 0 > Max: 2 > > > For the 1000...1100 range: > > Average: 0.7890625 > Std dev: 0.4964812206 > Min: 0 > Max: 2 > > > Looks like hash_32 is pretty good with small numbers. Yes hash_32 seems reasonable for the uid hash. With those long hash chains I wouldn't like to be on a machine with 10,000 processes with each with a different uid, and a processes calling setuid in the fast path. The uid hash that we are playing with is one that I sort of wish that the hash table could grow in size, so that we could scale up better. Aw well. Most of the time we only have a very small number of uids in play, so it doesn't matter at this point. Eric -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
