On Wed, Aug 28, 2024 at 11:52:27PM +0000, Eric Biggers wrote: > Thanks. We maybe should have included read/write separation in STATX_DIOALIGN, > but at the time the only case that was brought up was "DIO reads are supported > but DIO writes are not" which people had argued was not useful. > > Is this patch meant to support that case, Why would anyone support direct I/O reads but not writes? That seems really weird, but maybe I'm missing something important. > or just the case where DIO in both > directions is supported but with different alignments? Is that different file > offset alignments, different memory alignments, or both? This patch doesn't add > a stx_dio_read_mem_align field, so it's still assumed that both directions share > the existing stx_dio_mem_align property, including whether DIO is supported at > all (0 vs. nonzero). Yes. The memory alignment really is dependent on the underlying storage hardware DMA engine, which doesn't distinguish between reads and writes. > So as proposed, the only case it helps with is where DIO > in both directions is supported with the same memory alignment but different > file offset alignments. Yes. > Maybe that is intended, but it's not clear to me. Well, that's good feedback to make it more clear. > Are there specific userspace applications that would like to take advantage of a > smaller value of stx_dio_read_offset_align compared to the existing > stx_dio_offset_align? There are a lot of read-heavy workloads where smaller reads do make a difference.
