On 2017年11月20日 10:24, Chris Murphy wrote: > On Sun, Nov 19, 2017 at 7:13 PM, Qu Wenruo <quwenruo.bt...@gmx.com> wrote: >> >> >> On 2017年11月19日 14:17, Chris Murphy wrote: >>> fstrim should trim free space, but it only trims unallocated. This is >>> with kernel 4.14.0 and the entire 4.13 series. I'm pretty sure it >>> behaved this way with 4.12 also. >> >> Tested with 4.14-rc7, can't reproduce it. > > $ sudo btrfs fi us / > Overall: > Device size: 70.00GiB > Device allocated: 31.03GiB > Device unallocated: 38.97GiB > Device missing: 0.00B > Used: 22.12GiB > Free (estimated): 47.62GiB (min: 47.62GiB) > ...snip... > > $ sudo fstrim -v / > /: 39 GiB (41841328128 bytes) trimmed > > Then I run btrfs-debug -b / and find the least used block group, at 8% usage; > > block group offset 174202028032 len 1073741824 used 89206784 > chunk_objectid 256 flags 1 usage 0.08 > > And balance that block group: > > $ sudo btrfs balance start -dvrange=174202028032..174202028033 -dlimit=1 / > Done, had to relocate 1 out of 32 chunks > > And trim again: > > /: 39 GiB (41841328128 bytes) trimmed > > >> Any special mount options or setup? >> (BTW, I also tried space_cache=v2 and default v1, no obvious difference) > > > /dev/nvme0n1p8 on / type btrfs > (rw,relatime,seclabel,ssd,space_cache,subvolid=333,subvol=/root27)
Nothing special at all.
And unfortunately, no trace point inside btrfs_trim_block_group() at all.
But a quick glance shows me that, the loop to iterate existing block
groups to trim free space inside them has a return value overwrite bug.
So only unallocated space get trimmed.
Would you please try this diff to get the return value?
------
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 309a109069f1..dbec05dc8810 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10983,12 +10983,12 @@ int btrfs_trim_fs(struct btrfs_fs_info
*fs_info, struct fstrim_range *range)
ret = cache_block_group(cache, 0);
if (ret) {
btrfs_put_block_group(cache);
- break;
+ goto out;
}
ret = wait_block_group_cache_done(cache);
if (ret) {
btrfs_put_block_group(cache);
- break;
+ goto out;
}
}
ret = btrfs_trim_block_group(cache,
@@ -11000,7 +11000,7 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info,
struct fstrim_range *range)
trimmed += group_trimmed;
if (ret) {
btrfs_put_block_group(cache);
- break;
+ goto out;
}
}
@@ -11019,6 +11019,7 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info,
struct fstrim_range *range)
}
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+out:
range->len = trimmed;
return ret;
}
------
Thanks,
Qu
>
>
> Would a strace of fstrim help?
>
>
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