| Message ID | 20241127054737.33351-2-bharata@amd.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Large folios in block buffered IO path | expand |
On Wed, Nov 27, 2024 at 11:17:37AM +0530, Bharata B Rao wrote: > In order to experiment using large folios for block devices read/write > operations, expose an ioctl that userspace can selectively use on the > raw block devices. > > For the write path, this forces iomap layer to provision large > folios (via iomap_file_buffered_write()). Well, unless CONFIG_BUFFER_HEAD is disabled, the block device uses the buffer head based write path, which currently doesn't fully support large folios (although there is series out to do so on fsdevel right now), so I don't think this will fully work. But the more important problem, and the reason why we don't use the non-buffer_head path by default is that the block device mapping is reused by a lot of file systems, which are not aware of large folios, and will get utterly confused. So if we want to do anything smart on the block device mapping, we'll have to ensure we're back to state compatible with these file systems before calling into their mount code, and stick to the old code while file systems are mounted. Of course the real question is: why do you care about buffered I/O performance on the block device node?
diff --git a/block/ioctl.c b/block/ioctl.c index 6554b728bae6..6af26a08ef34 100644 --- a/block/ioctl.c +++ b/block/ioctl.c @@ -548,6 +548,12 @@ static int blkdev_bszset(struct file *file, blk_mode_t mode, return ret; } +static int blkdev_set_large_folio(struct block_device *bdev) +{ + mapping_set_large_folios(bdev->bd_mapping); + return 0; +} + /* * Common commands that are handled the same way on native and compat * user space. Note the separate arg/argp parameters that are needed @@ -632,6 +638,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode, return blkdev_pr_preempt(bdev, mode, argp, true); case IOC_PR_CLEAR: return blkdev_pr_clear(bdev, mode, argp); + case BLKSETLFOLIO: + return blkdev_set_large_folio(bdev); default: return -ENOIOCTLCMD; } diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 753971770733..5c8a326b68a1 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -203,6 +203,8 @@ struct fsxattr { #define BLKROTATIONAL _IO(0x12,126) #define BLKZEROOUT _IO(0x12,127) #define BLKGETDISKSEQ _IOR(0x12,128,__u64) +#define BLKSETLFOLIO _IO(0x12, 129) + /* * A jump here: 130-136 are reserved for zoned block devices * (see uapi/linux/blkzoned.h)
In order to experiment using large folios for block devices read/write operations, expose an ioctl that userspace can selectively use on the raw block devices. For the write path, this forces iomap layer to provision large folios (via iomap_file_buffered_write()). Signed-off-by: Bharata B Rao <bharata@amd.com> --- block/ioctl.c | 8 ++++++++ include/uapi/linux/fs.h | 2 ++ 2 files changed, 10 insertions(+)