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?
