On 5/26/21 1:58 PM, Jim Guo wrote: >> 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. > OK. And I would suggest to start your work on upstream bcache code. Coly Li > 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
