The four big issues I've seen regarding it are: 1. TRIM/DISCARD support is broken as a (partial?) result of this.2. It appears to expose underlying issues with the defrag code (stuff ending up more fragmented after defrag). 3. Since upgrading to a kernel with this patch, most of the BTRFS filesystems that I have that are very rewrite heavy have gotten very noticeably slower that they were beforehand (and this goes away when I run them on a kernel without auto-reclaim). 4. All of my filesystems are experiencing seemingly non-deterministic delays around most large scale VFS level operations (eg, deleting or relocating lots of files)
While I understand that this feature does solve (at least partially) an very real issue with BTRFS, there were a number of people who never had this issue to begin with because we ran regular balance operations on our filesystems.
Based on this, I would like to propose that some method be provided to disable auto-reclaim be added. Personally, I would prefer to leave it as the default and have a mount option to disable it.
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