On Thu, Jan 21, 2021 at 06:49:39PM +0530, Gautham Ananthakrishna wrote: > We tested this patch set recently and found it limiting negative dentry to a > small part of total memory. The following is the test result we ran on two > types of servers, one is 256G memory with 24 CPUS and another is 3T memory > with 384 CPUS. The test case is using a lot of processes to generate negative > dentry in parallel, the following is the test result after 72 hours, the > negative dentry number is stable around that number even after running longer > for much longer time. Without the patch set, in less than half an hour 197G was > taken by negative dentry on 256G system, in 1 day 2.4T was taken on 3T system. > > system memory neg-dentry-number neg-dentry-mem-usage > 256G 55259084 10.6G > 3T 202306756 38.8G > > For perf test, we ran the following, and no regression found. > > 1. create 1M negative dentry and then touch them to convert them to positive > dentry > > 2. create 10K/100K/1M files > > 3. remove 10K/100K/1M files > > 4. kernel compile Good for you; how would that work for thinner boxen, though? I agree that if you have 8M hash buckets your "no more than 3 unused negatives per bucket" is generous enough for everything, but that's less obvious for something with e.g 4 or 8 gigs. And believe it or not, there are real-world boxen like that ;-)
