Hi, > # dmesg |grep EXT4-fs |tail -1 > [ 1594.829833] EXT4-fs (nvme0n1p1): mounted filesystem with ordered > data mode. Opts: data=ordered,discard > # blktrace /dev/nvme0n1 & sleep 1 ; time rm -rf /media/linux-5.10/ ; kill $! > [1] 3032 > > real 0m1.328s > user 0m0.063s > sys 0m1.231s > # === nvme0n1 === > CPU 0: 0 events, 0 KiB data > CPU 1: 0 events, 0 KiB data > CPU 2: 0 events, 0 KiB data > CPU 3: 1461 events, 69 KiB data > CPU 4: 1 events, 1 KiB data > CPU 5: 0 events, 0 KiB data > CPU 6: 0 events, 0 KiB data > CPU 7: 0 events, 0 KiB data > Total: 1462 events (dropped 0), 69 KiB data > > > # dmesg |grep EXT4-fs |tail -1 > [ 1734.837651] EXT4-fs (nvme0n1p1): mounted filesystem with writeback > data mode. Opts: data=writeback,discard > # blktrace /dev/nvme0n1 & sleep 1 ; time rm -rf /media/linux-5.10/ ; kill $! > [1] 3069 > > real 1m30.273s > user 0m0.139s > sys 0m3.084s > # === nvme0n1 === > CPU 0: 133830 events, 6274 KiB data > CPU 1: 21878 events, 1026 KiB data > CPU 2: 46365 events, 2174 KiB data > CPU 3: 98116 events, 4600 KiB data > CPU 4: 290902 events, 13637 KiB data > CPU 5: 10926 events, 513 KiB data > CPU 6: 76861 events, 3603 KiB data > CPU 7: 17855 events, 837 KiB data > Total: 696733 events (dropped 0), 32660 KiB data > In this result, there is few IO in ordered mode. As I understand (please correct this if I am wrong), with writeback + discard, ext4_issue_discard is called immediately at each rm command. However, with ordered mode, ext4_issue_discard is called when end of committing a transaction to pace with the corresponding transaction. It means, they are not discarded yet. Even with ordered mode, if sync is called after rm command, ext4_issue_discard can be called due to transaction commit. So, I think you will get similar results form writeback mode with sync command. Thanks, Daejun
