On 09/09/16 12:18, Holger Hoffstätte wrote: > On Fri, 09 Sep 2016 16:17:48 +0800, Wang Xiaoguang wrote: > >> cleaner_kthread() may run at any time, in which it'll call >> btrfs_delete_unused_bgs() >> to delete unused block groups. Because this work is asynchronous, it may >> also result >> in false ENOSPC error. > <snip> > > With this v3 I can now no longer balance (tested only with metadata). > New chunks are allocated (as balance does) but nothing ever shrinks, until > after unmount/remount, when the cleaner eventually kicks in. > > This might be related to the recent patch by Naohiro Aota: > "btrfs: let btrfs_delete_unused_bgs() to clean relocated bgs" > > which by itself doesn't seem to do any harm (i.e. everything still seems > to work as expected).
Actually even that is not true; both patches seem to be wrong in subtle ways. Naohiro's patch seems to prevent the deletion during balance, whereas yours prevents the cleaner from kicking in. As a simple reproducer you can convert from -mdup to -msingle (to create bloat) and then balance with -musage=10. Depending on which of the two patches are applied, you end with bloat that only grows and never shrinks, or bloat that ends up in mixed state (dup and single). Undoing both makes both balancing and cleaning work again. -h -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
