On Wed, May 27, 2020 at 11:32:02AM +0200, Reindl Harald wrote: > > > Am 27.05.20 um 11:19 schrieb Lukas Czerner: > > On Wed, May 27, 2020 at 04:38:50PM +0900, Wang Shilong wrote: > >> From: Wang Shilong <wshilong@xxxxxxx> > >> > >> Currently WAS_TRIMMED flag is not persistent, whenever filesystem was > >> remounted, fstrim need walk all block groups again, the problem with > >> this is FSTRIM could be slow on very large LUN SSD based filesystem. > >> > >> To avoid this kind of problem, we introduce a block group flag > >> EXT4_BG_WAS_TRIMMED, the side effect of this is we need introduce > >> extra one block group dirty write after trimming block group. > > would that also fix the issue that *way too much* is trimmed all the > time, no matter if it's a thin provisioned vmware disk or a phyiscal > RAID10 with SSD no, the mechanism remains the same, but the proposal is to make it pesisten across re-mounts. > > no way of 315 MB deletes within 2 hours or so on a system with just 485M > used The reason is that we're working on block group granularity. So if you have almost free block group, and you free some blocks from it, the flag gets freed and next time you run fstrim it'll trim all the free space in the group. Then again if you free some blocks from the group, the flags gets cleared again ... But I don't think this is a problem at all. Certainly not worth tracking free/trimmed extents to solve it. > > [root@firewall:~]$ fstrim -av > /boot: 0 B (0 bytes) trimmed on /dev/sda1 > /: 315.2 MiB (330522624 bytes) trimmed on /dev/sdb1 The solution is to run fstrim less often, that's the whole point of the fstrim. If you need to run it more often, then you probably want to use -o discard mount option. -Lukas > > [root@firewall:~]$ df > Filesystem Type Size Used Avail Use% Mounted on > /dev/sdb1 ext4 5.8G 463M 5.4G 8% / > /dev/sda1 ext4 485M 42M 440M 9% /boot >
