On Mon, 4 Nov 2019, Alessio Balsini wrote: > > > -- Alignment > > > > > > Our approach follows the solution proposed by Mikulas [1]. > > > Being the block alignment of file extents automatically managed by the > > > filesystem, using FIEMAP should have no alignment-related performance issue. > > > But in our implementation we hit a misalignment [2] branch which leads to > > > dmwarning messages [3, 4]. > > > > > > I have a limited experience with the block layer and dm, so I'm still > > > struggling in finding the root cause for this, either in user space or kernel > > > space. > > > > I don't know. What is the block size of the filesystem? Are all mappings > > aligned to this block size? > > Here follows a just generated warning coming from a Pixel 4 kernel (4.14): > > [ 3093.443808] device-mapper: table: 253:16: adding target device dm-15 > caused an alignment inconsistency: physical_block_size=4096, > logical_block_size=4096, alignment_offset=61440, start=0 > > Does this contain all the info you asked for? Look at the function blk_stack_limits - it has various checks that make it return -1. Insert some debugging printk's there and find out which check made the function return -1. Based on this, we can find out which of the limits triggered the error message. > I started investigating this issue, but since we didn't notice any > performance degradation, I prioritized other things. I'll be hopefully > able to get back to this warning in the next months. > Please let me know if I can help you with that or if you need additional > information. Mikulas
