On Thu, Oct 18, 2018 at 07:03:42AM -0700, Matthew Wilcox wrote: > Before we go down this road, could we have a discussion about what > hardware actually requires this? Storage has this weird assumption that > I/Os must be at least 512 byte aligned in memory, and I don't know where > this idea comes from. Network devices can do arbitrary byte alignment. > Even USB controllers can do arbitrary byte alignment. Sure, performance > is going to suck and there are definite risks on some architectures > with doing IOs that are sub-cacheline aligned, but why is storage such a > special snowflake that we assume that host controllers are only capable > of doing 512-byte aligned DMAs? Actually most storage controllers requires 4-byte alignment, but there is a significant subset that requires 512-byte alignment.
