On 1.04.19 г. 21:44 ч., David Sterba wrote: > On Wed, Mar 27, 2019 at 02:24:16PM +0200, Nikolay Borisov wrote: >> Currently unallocated chunks are always trimmed. For example >> 2 consecutive trims on large storage would trim freespace twice >> irrespective of whether the space was actually allocated or not between >> those trims. >> >> Optimise this behavior by exploiting the newly introduced alloc_state >> tree of btrfs_device. A new CHUNK_TRIMMED bit is used to mark >> those unallocated chunks which have been trimmed and have not been >> allocated afterwards. On chunk allocation the respective underlying devices' >> physical space will have its CHUNK_TRIMMED flag cleared. This avoids >> submitting discards for space which hasn't been changed since the last >> time discard was issued. > > This means during one mount, right? Because the state is not recorded > on-disk anywhere. This also means that a complete unmount / mount > followed by trim will do the discard on the freed blocks again. I don't > thik there's anything wrong with that, just that this should be put to > the docs. Correct, on unmount btrfs_close_devices is called which frees trim state. >
