Commits
Mike Snitzer committed d200c30ef00
dm thin: fix pool_io_hints to avoid looking at max_hw_sectors Simplify the pool_io_hints code that works to establish a max_sectors value that is a power-of-2 factor of the thin-pool's blocksize. The biggest associated improvement is that the DM thin-pool is no longer concerning itself with the data device's max_hw_sectors when adjusting max_sectors. This fixes the relative fragility of the original "dm thin: adjust max_sectors_kb based on thinp blocksize" commit that only became apparent when testing was performed using a DM thin-pool ontop of a virtio_blk device. One proposed upstream patch detailed the problems inherent in virtio_blk: https://lkml.org/lkml/2014/11/20/611 So even though virtio_blk incorrectly set its max_hw_sectors it actually helped make it clear that we need DM thinp to be tolerant of any future Linux driver that incorrectly sets max_hw_sectors. We only need to be concerned with modifying the thin-pool device's max_sectors limit if it is smaller than the thin-pool's blocksize. In this case the value of max_sectors does become a limiting factor when upper layers (e.g. filesystems) construct their bios. But if the hardware can support IOs larger than the thin-pool's blocksize the user is encouraged to adjust the thin-pool's data device's max_sectors accordingly -- doing so will enable the thin-pool to inherit the established user-defined max_sectors. Signed-off-by: Mike Snitzer <snitzer@redhat.com>