On Thu, 2024-04-18 at 16:51 +0200, Christoph Hellwig wrote: > > > > Note that we really should not stack max_sectors anyway, as it's > > > only > > > used for splitting in the lower device to start with. > > > > If that's the case, why don't we inhibit the modification for > > max_sectors > > on the lower devices? > > Why would we? It makes absolutly no sense to inherit these limits, > the lower device will split anyway which is very much the point of > the immutable bio_vec work. > Sorry, I don't follow. With (request-based) dm-multipath on top of SCSI, we hit the "over max size limit" condition in blk_insert_cloned_request() [1], which will cause IO to fail at the dm level. So at least in this configuration, it's crucial that the upper device inherit the lower device's limits. Regards, Martin [1] https://elixir.bootlin.com/linux/latest/source/block/blk-mq.c#L3048
