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block: relax direct io memory alignment

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Use the address alignment requirements from the block_device for direct
io instead of requiring addresses be aligned to the block size. User
space can discover the alignment requirements from the dma_alignment
queue attribute.

User space can specify any hardware compatible DMA offset for each
segment, but every segment length is still required to be a multiple of
the block size.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220610195830.3574005-11-kbusch@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Keith Busch 2022-06-10 12:58:29 -07:00 committed by Jens Axboe
parent 5debd9691c
commit b1a000d3b8
3 changed files with 16 additions and 2 deletions
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9
block/bio.c
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@ -1220,7 +1220,16 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
/*
* Each segment in the iov is required to be a block size multiple.
* However, we may not be able to get the entire segment if it spans
* more pages than bi_max_vecs allows, so we have to ALIGN_DOWN the
* result to ensure the bio's total size is correct. The remainder of
* the iov data will be picked up in the next bio iteration.
*/
size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
if (size > 0)
size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));
if (unlikely(size <= 0))
return size ? size : -EFAULT;

4
block/fops.c
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@ -45,8 +45,8 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb)
static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
struct iov_iter *iter)
{
return ((pos | iov_iter_alignment(iter)) &
(bdev_logical_block_size(bdev) - 1));
return pos & (bdev_logical_block_size(bdev) - 1) ||
!bdev_iter_is_aligned(bdev, iter);
}
#define DIO_INLINE_BIO_VECS 4

5
include/linux/blkdev.h
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@ -424,6 +424,11 @@ struct request_queue {
unsigned long nr_requests; /* Max # of requests */
unsigned int dma_pad_mask;
/*
* Drivers that set dma_alignment to less than 511 must be prepared to
* handle individual bvec's that are not a multiple of a SECTOR_SIZE
* due to possible offsets.
*/
unsigned int dma_alignment;
#ifdef CONFIG_BLK_INLINE_ENCRYPTION