Re: [PATCH 06/16] iomap: support block size > page size for direct IO

[Nikolay Borisov <nborisov@suse.com>]

On 7.11.18 г. 8:31 ч., Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> iomap_dio_rw() has all the infrastructure in place to support block
> size > page size filesystems because it is essentially just
> sub-block DIO. It needs help, however, with the sub-block zeroing
> code (needs multi-page IOs) page cache invalidation over the block
> being written.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/iomap.c | 65 ++++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 49 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 16d16596b00f..8878b1f1f9c7 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -1548,21 +1548,34 @@ static void iomap_dio_bio_end_io(struct bio *bio)
>  	}
>  }
>  
> +/*
> + * With zeroing for block size larger than page size, the zeroing length can
> + * span multiple pages.
> + */
> +#define howmany(x, y) (((x)+((y)-1))/(y))

nit: This could be replaced by DIV_ROUND_UP

>  static blk_qc_t
>  iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
>  		unsigned len)
>  {
>  	struct page *page = ZERO_PAGE(0);
>  	struct bio *bio;
> +	int npages = howmany(len, PAGE_SIZE);
> +
> +	WARN_ON_ONCE(npages > 16);
>  
> -	bio = bio_alloc(GFP_KERNEL, 1);
> +	bio = bio_alloc(GFP_KERNEL, npages);
>  	bio_set_dev(bio, iomap->bdev);
>  	bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
>  	bio->bi_private = dio;
>  	bio->bi_end_io = iomap_dio_bio_end_io;
>  
> -	get_page(page);
> -	__bio_add_page(bio, page, len, 0);
> +	while (npages-- > 0) {
> +		unsigned plen = min_t(unsigned, PAGE_SIZE, len);
> +		get_page(page);
> +		__bio_add_page(bio, page, plen, 0);
> +		len -= plen;
> +	}
> +	WARN_ON(len != 0);
>  	bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE);
>  
>  	atomic_inc(&dio->ref);
> @@ -1752,6 +1765,38 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
>  	}
>  }
>  
> +/*
> + * This is lifted almost straight from xfs_flush_unmap_range(). Need a generic
> + * version of the block size rounding for these purposes.
> + */
> +static int
> +iomap_flush_unmap_range(struct file *f, loff_t offset, loff_t len)
> +{
> +	struct inode *inode = file_inode(f);
> +	loff_t rounding, start, end;
> +	int ret;
> +
> +	rounding = max_t(loff_t, i_blocksize(inode), PAGE_SIZE);
> +	start = round_down(offset, rounding);
> +	end = round_up(offset + len, rounding) - 1;
> +
> +	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Try to invalidate cache pages for the range we're direct
> +	 * writing.  If this invalidation fails, tough, the write will
> +	 * still work, but racing two incompatible write paths is a
> +	 * pretty crazy thing to do, so we don't support it 100%.
> +	 */
> +	ret = invalidate_inode_pages2_range(inode->i_mapping,
> +			start >> PAGE_SHIFT, end >> PAGE_SHIFT);
> +	if (ret)
> +		dio_warn_stale_pagecache(f);
> +	return 0;
> +}
> +
>  /*
>   * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO
>   * is being issued as AIO or not.  This allows us to optimise pure data writes
> @@ -1829,22 +1874,10 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  		flags |= IOMAP_NOWAIT;
>  	}
>  
> -	ret = filemap_write_and_wait_range(mapping, start, end);
> +	ret = iomap_flush_unmap_range(iocb->ki_filp, start, end);
>  	if (ret)
>  		goto out_free_dio;
>  
> -	/*
> -	 * Try to invalidate cache pages for the range we're direct
> -	 * writing.  If this invalidation fails, tough, the write will
> -	 * still work, but racing two incompatible write paths is a
> -	 * pretty crazy thing to do, so we don't support it 100%.
> -	 */
> -	ret = invalidate_inode_pages2_range(mapping,
> -			start >> PAGE_SHIFT, end >> PAGE_SHIFT);
> -	if (ret)
> -		dio_warn_stale_pagecache(iocb->ki_filp);
> -	ret = 0;
> -
>  	if (iov_iter_rw(iter) == WRITE && !dio->wait_for_completion &&
>  	    !inode->i_sb->s_dio_done_wq) {
>  		ret = sb_init_dio_done_wq(inode->i_sb);
>