On 2/11/22 3:40 AM, Chaitanya Kulkarni wrote: > On 2/10/22 10:11 PM, Eric Biggers wrote: >> From: Eric Biggers <ebiggers@xxxxxxxxxx> >> >> Traditionally, the conditions for when DIO (direct I/O) is supported >> were fairly simple: filesystems either supported DIO aligned to the >> block device's logical block size, or didn't support DIO at all. >> >> However, due to filesystem features that have been added over time (e.g, >> data journalling, inline data, encryption, verity, compression, >> checkpoint disabling, log-structured mode), the conditions for when DIO >> is allowed on a file have gotten increasingly complex. Whether a >> particular file supports DIO, and with what alignment, can depend on >> various file attributes and filesystem mount options, as well as which >> block device(s) the file's data is located on. >> >> XFS has an ioctl XFS_IOC_DIOINFO which exposes this information to >> applications. However, as discussed >> (https://lore.kernel.org/linux-fsdevel/20220120071215.123274-1-ebiggers@xxxxxxxxxx/T/#u), >> this ioctl is rarely used and not known to be used outside of >> XFS-specific code. It also was never intended to indicate when a file >> doesn't support DIO at all, and it only exposes the minimum I/O >> alignment, not the optimal I/O alignment which has been requested too. >> >> Therefore, let's expose this information via statx(). Add the >> STATX_IOALIGN flag and three fields associated with it: >> >> * stx_mem_align_dio: the alignment (in bytes) required for user memory >> buffers for DIO, or 0 if DIO is not supported on the file. >> >> * stx_offset_align_dio: the alignment (in bytes) required for file >> offsets and I/O segment lengths for DIO, or 0 if DIO is not supported >> on the file. This will only be nonzero if stx_mem_align_dio is >> nonzero, and vice versa. >> >> * stx_offset_align_optimal: the alignment (in bytes) suggested for file >> offsets and I/O segment lengths to get optimal performance. This >> applies to both DIO and buffered I/O. It differs from stx_blocksize >> in that stx_offset_align_optimal will contain the real optimum I/O >> size, which may be a large value. In contrast, for compatibility >> reasons stx_blocksize is the minimum size needed to avoid page cache >> read/write/modify cycles, which may be much smaller than the optimum >> I/O size. For more details about the motivation for this field, see >> https://lore.kernel.org/r/20220210040304.GM59729@xxxxxxxxxxxxxxxxxxx >> >> Note that as with other statx() extensions, if STATX_IOALIGN isn't set >> in the returned statx struct, then these new fields won't be filled in. >> This will happen if the filesystem doesn't support STATX_IOALIGN, or if >> the file isn't a regular file. (It might be supported on block device >> files in the future.) It might also happen if the caller didn't include >> STATX_IOALIGN in the request mask, since statx() isn't required to >> return information that wasn't requested. >> >> This commit adds the VFS-level plumbing for STATX_IOALIGN. Individual >> filesystems will still need to add code to support it. >> >> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> >> --- > > > I've actually worked on similar series to export alignment and > granularity for non-trivial operations, this implementation > only exporting I/O alignments (mostly REQ_OP_WRITE/REQ_OP_READ) via > stax. > > Since it is coming from :- > bdev_logical_block_size()->q->limits.logical_block_size that is set when > low level driver like nvme calls blk_queue_logical_block_size(). > > From my experience especially with SSDs, applications want to > know similar information about different non-trivial requests such as > REQ_OP_DISCARD/REQ_OP_WRITE_ZEROES/REQ_OP_VERIFY (work in progress see > [1]) etc. > > It will be great to make this generic userspace interface where user can > ask for specific REQ_OP_XXX such as generic I/O REQ_OP_READ/REQ_OP_WRITE > and non generic REQ_OP_XX such as REQ_OP_DISCARD/REQ_OP_VERIFY etc .... > > Since I've worked on implementing REQ_OP_VERIFY support I don't want to > implement separate interface for querying the REQ_OP_VERIFY or any other > non-trivial REQ_OP_XXX granularity or alignment. > > -ck > > [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Flinux-xfs%2Fmsg56826.html&data=04%7C01%7Cchaitanyak%40nvidia.com%7C252d78e009ad49bd522208d9ed534dcf%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637801764313014840%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=1owqIDlcst4h%2FGr9Azteaiy22vfHFZojRipKmk6A%2FCg%3D&reserved=0 > Adding right link for REQ_OP_VERIFY ... [1] https://www.spinics.net/lists/linux-xfs/msg56826.html
