On Thu 14-12-23 21:06:46, yebin (H) wrote: > > > On 2023/12/14 16:58, Jan Kara wrote: > > On Thu 14-12-23 14:46:35, Ye Bin wrote: > > > There will not issue discard cmd when do segment fstrim for ext4 fs, however, > > > if full fstrim for the same fs will issue discard cmd. > > > Above issue may happens as follows: > > > Precondition: > > > 1. Fstrim range [0, 15] and [16, 31]; > > > 2. Discard granularity is 16; > > > Range1 Range2 > > > 1111000000000000 0000111010101011 > > > There's no free space length large or equal than 16 in 'Range1' or 'Range2'. > > > As ext4_try_to_trim_range() only search free space among range which user > > > specified. However, there's maximum free space length 16 in 'Range1'+ 'Range2'. > > > To solve above issue, we need to find the longest free space to discard. > > > > > > Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx> > > OK, I agree that there is this behavioral difference. However is that a > > practical problem? I mean I would not expect the range to be particularly > > small, rather something like 1GB and then these boundary conditions don't > > really matter. This is also sensible so that we can properly track whether > > the whole block group was trimmed or not. Finally I'd also argue that > > trimming outside of specified range might be unexpected for the user. So a > > *fix* for this in my opinion lays in userspace which needs to select > > sensible ranges to use for trimming. > > > > Honza > Thanks for your reply. > Our product fstrim entire file system, found to take a long time, thus > affecting other processes. > So they want to segment the file system fstrim based on the IO of the > system. But they found > that fragmented fstrims didn't work the same as fstrim for the entire file > system. > Users do not know the distribution of free blocks in the file system, and > they do not know the > reasonable range. The user's simple perception is that the effect of > segmented fstrim and full > fstrim should be consistent. > I researched the implementation of fstrim on the XFS file system, and for > the scenario described > in my patch, the results of both operations are consistent. OK, we've discussed this on yesterday's ext4 call and we've came to a conclusion that we don't care that much and consistency among filesystems is good so I'll go back and review your patch. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
