> What is the kernel version in your system? And where the kernel package > is from? I am using kernel version 4.19.142, I compile it from source code downloaded from kernel.org. > Do you have a testing result on this idea? Sorry, the testing environment is not owned by me and I did not keep any testing result currently. I will test for this later in my own testing environment. Coly Li <colyli@xxxxxxx> 于2021年5月17日周一 下午7:53写道： > > On 5/17/21 11:54 AM, Jim Guo wrote: > > Hello, Mr. Li. > > Recently I was experiencing frequent io hang when testing with fio > > with 4K random write. Fio iops dropped to 0 for about 20 seconds > > every several minutes. > > After some debugging, I discovered that it is the incremental gc that > > cause this problem. > > My cache disk is relatively small (375GiB with 4K block size and 512K > > bucket size), backing hdds are 4 x 1 TiB. I cannot reproduce this on > > another environment with bigger cache disk. > > When running 4K random write fio bench, the buckets are consumed very > > quickly and soon it has to invalidate some bucket (this happens quite > > often). Since the cache disk is small, a lot of write io will soon > > reach sectors_to_gc and trigger gc thread. Write io will also increase > > search_inflight, which cause gc thread to sleep for 100ms. This will > > cause gc procedure to execute for a long time, and invalidating bucket > > for the write io will wait for the whole gc procedure. > > After removing the 100ms sleep from the incremental gc patch, the io > > never hang any more. > > What is the kernel version in your system? And where the kernel package > is from? > > > > I think for small ssd, sleeping for 100ms seems too long or maybe > > write io should not trigger gc thread to sleep for 100ms? > > Thank you very much. > > > > Do you have a testing result on this idea? > > > Thanks. > > Coly Li
