On Mon, Feb 19, 2024 at 01:01:08PM +0000, John Garry wrote: > From: Alan Adamson <alan.adamson@xxxxxxxxxx> > > Add support to set block layer request_queue atomic write limits. The > limits will be derived from either the namespace or controller atomic > parameters. > > NVMe atomic-related parameters are grouped into "normal" and "power-fail" > (or PF) class of parameter. For atomic write support, only PF parameters > are of interest. The "normal" parameters are concerned with racing reads > and writes (which also applies to PF). See NVM Command Set Specification > Revision 1.0d section 2.1.4 for reference. > > Whether to use per namespace or controller atomic parameters is decided by > NSFEAT bit 1 - see Figure 97: Identify - Identify Namespace Data Structure, > #NVM Command Set. > > NVMe namespaces may define an atomic boundary, whereby no atomic guarantees > are provided for a write which straddles this per-lba space boundary. The > block layer merging policy is such that no merges may occur in which the > resultant request would straddle such a boundary. > > Unlike SCSI, NVMe specifies no granularity or alignment rules. In addition, > again unlike SCSI, there is no dedicated atomic write command - a write > which adheres to the atomic size limit and boundary is implicitly atomic. > > If NSFEAT bit 1 is set, the following parameters are of interest: > - NAWUPF (Namespace Atomic Write Unit Power Fail) > - NABSPF (Namespace Atomic Boundary Size Power Fail) > - NABO (Namespace Atomic Boundary Offset) > > and we set request_queue limits as follows: > - atomic_write_unit_max = rounddown_pow_of_two(NAWUPF) > - atomic_write_max_bytes = NAWUPF > - atomic_write_boundary = NABSPF > > If in the unlikely scenario that NABO is non-zero, then atomic writes will > not be supported at all as dealing with this adds extra complexity. This > policy may change in future. > > In all cases, atomic_write_unit_min is set to the logical block size. > > If NSFEAT bit 1 is unset, the following parameter is of interest: > - AWUPF (Atomic Write Unit Power Fail) > > and we set request_queue limits as follows: > - atomic_write_unit_max = rounddown_pow_of_two(AWUPF) > - atomic_write_max_bytes = AWUPF > - atomic_write_boundary = 0 > > The block layer requires that the atomic_write_boundary value is a > power-of-2. However, it is really only required that atomic_write_boundary > be a multiple of atomic_write_unit_max. As such, if NABSPF were not a > power-of-2, atomic_write_unit_max could be reduced such that it was > divisible into NABSPF. However, this complexity will not be yet supported. > > A helper function, nvme_valid_atomic_write(), is also added for the > submission path to verify that a request has been submitted to the driver > will actually be executed atomically. Maybe patch 11 should be folded into this one. No bigged, the series as a whole looks good. Reviewed-by: Keith Busch <kbusch@xxxxxxxxxx>
