On 4/12/24 11:16 AM, Christoph Lameter (Ampere) wrote: > On Fri, 12 Apr 2024, Jianfeng Wang wrote: > >>>> Can you run some tests showing the difference between the estimation and >>>> the real count? >> >> Yes. >> On a server with one NUMA node, I create a case that uses many dentry objects. >> For "dentry", the length of partial slabs is slightly above 250000. Then, I >> compare my approach of scanning N slabs from the list's head v.s. the original >> approach of scanning the full list. I do it by getting both results using >> the new and the original count_partial() and printing them in /proc/slabinfo. >> >> N = 10000 >> my_result = 4741651 >> org_result = 4744966 >> diff = (org_result - my_result) / org_result = 0.00069 = 0.069 % >> >> Increasing N further to 25000 will only slight improve the accuracy: >> N = 15000 -> diff = 0.02 % >> N = 20000 -> diff = 0.01 % >> N = 25000 -> diff = -0.017 % >> >> Based on the measurement, I think the difference between the estimation and >> the real count is very limited (i.e. less than 0.1% for N = 10000). The >> benefit is significant: shorter execution time for get_slabinfo(); no more >> soft lockups or crashes caused by count_partial(). > > Wow. That is good. Maybe decrease N to 1000 instead? > Yes, the diff is still limited. Here are some numbers: N = 5000 -> diff = 0.0019 = 0.19 % N = 3000 -> diff = 0.0023 = 0.23 % N = 1000 -> diff = 0.0040 = 0.40 % So, the estimation is quite accurate.
