Re: [PATCH v6 01/13] iomap: inline iomap_dio_bio_opflags()

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

John Garry <john.g.garry@oracle.com> writes:

> It is neater to build blk_opf_t fully in one place, so inline
> iomap_dio_bio_opflags() in iomap_dio_bio_iter().
>
> Also tidy up the logic in dealing with IOMAP_DIO_CALLER_COMP, in generally
> separate the logic in dealing with flags associated with reads and writes.
>

Indeed it clean things up and separates the logic required for
IOMAP_DIO_WRITE v/s reads.

The change looks good to me. Please feel free to add -
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>


> Originally-from: Christoph Hellwig <hch@lst.de>
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
> Should I change author?
>  fs/iomap/direct-io.c | 112 +++++++++++++++++++------------------------
>  1 file changed, 49 insertions(+), 63 deletions(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 5299f70428ef..8c1bec473586 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -312,27 +312,20 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
>  }
>  
>  /*
> - * Figure out the bio's operation flags from the dio request, the
> - * mapping, and whether or not we want FUA.  Note that we can end up
> - * clearing the WRITE_THROUGH flag in the dio request.
> + * Use a FUA write if we need datasync semantics and this is a pure data I/O
> + * that doesn't require any metadata updates (including after I/O completion
> + * such as unwritten extent conversion) and the underlying device either
> + * doesn't have a volatile write cache or supports FUA.
> + * This allows us to avoid cache flushes on I/O completion.
>   */
> -static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
> -		const struct iomap *iomap, bool use_fua, bool atomic_hw)
> +static inline bool iomap_dio_can_use_fua(const struct iomap *iomap,
> +		struct iomap_dio *dio)
>  {
> -	blk_opf_t opflags = REQ_SYNC | REQ_IDLE;
> -
> -	if (!(dio->flags & IOMAP_DIO_WRITE))
> -		return REQ_OP_READ;
> -
> -	opflags |= REQ_OP_WRITE;
> -	if (use_fua)
> -		opflags |= REQ_FUA;
> -	else
> -		dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
> -	if (atomic_hw)
> -		opflags |= REQ_ATOMIC;
> -
> -	return opflags;
> +	if (iomap->flags & (IOMAP_F_SHARED | IOMAP_F_DIRTY))
> +		return false;
> +	if (!(dio->flags & IOMAP_DIO_WRITE_THROUGH))
> +		return false;
> +	return !bdev_write_cache(iomap->bdev) || bdev_fua(iomap->bdev);
>  }
>  
>  static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
> @@ -340,52 +333,59 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  	const struct iomap *iomap = &iter->iomap;
>  	struct inode *inode = iter->inode;
>  	unsigned int fs_block_size = i_blocksize(inode), pad;
> -	bool atomic_hw = iter->flags & IOMAP_ATOMIC_HW;
>  	const loff_t length = iomap_length(iter);
>  	loff_t pos = iter->pos;
> -	blk_opf_t bio_opf;
> +	blk_opf_t bio_opf = REQ_SYNC | REQ_IDLE;
>  	struct bio *bio;
>  	bool need_zeroout = false;
> -	bool use_fua = false;
>  	int nr_pages, ret = 0;
>  	u64 copied = 0;
>  	size_t orig_count;
>  
> -	if (atomic_hw && length != iter->len)
> -		return -EINVAL;
> -
>  	if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1) ||
>  	    !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
>  		return -EINVAL;
>  
> -	if (iomap->type == IOMAP_UNWRITTEN) {
> -		dio->flags |= IOMAP_DIO_UNWRITTEN;
> -		need_zeroout = true;
> -	}
> +	if (dio->flags & IOMAP_DIO_WRITE) {
> +		bio_opf |= REQ_OP_WRITE;
> +
> +		if (iter->flags & IOMAP_ATOMIC_HW) {
> +			if (length != iter->len)
> +				return -EINVAL;
> +			bio_opf |= REQ_ATOMIC;
> +		}
> +
> +		if (iomap->type == IOMAP_UNWRITTEN) {
> +			dio->flags |= IOMAP_DIO_UNWRITTEN;
> +			need_zeroout = true;
> +		}
>  
> -	if (iomap->flags & IOMAP_F_SHARED)
> -		dio->flags |= IOMAP_DIO_COW;
> +		if (iomap->flags & IOMAP_F_SHARED)
> +			dio->flags |= IOMAP_DIO_COW;
> +
> +		if (iomap->flags & IOMAP_F_NEW) {
> +			need_zeroout = true;
> +		} else if (iomap->type == IOMAP_MAPPED) {
> +			if (iomap_dio_can_use_fua(iomap, dio))
> +				bio_opf |= REQ_FUA;
> +			else
> +				dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
> +		}
>  
> -	if (iomap->flags & IOMAP_F_NEW) {
> -		need_zeroout = true;
> -	} else if (iomap->type == IOMAP_MAPPED) {
>  		/*
> -		 * Use a FUA write if we need datasync semantics, this is a pure
> -		 * data IO that doesn't require any metadata updates (including
> -		 * after IO completion such as unwritten extent conversion) and
> -		 * the underlying device either supports FUA or doesn't have
> -		 * a volatile write cache. This allows us to avoid cache flushes
> -		 * on IO completion. If we can't use writethrough and need to
> -		 * sync, disable in-task completions as dio completion will
> -		 * need to call generic_write_sync() which will do a blocking
> -		 * fsync / cache flush call.
> +		 * We can only do deferred completion for pure overwrites that
> +		 * don't require additional I/O at completion time.
> +		 *
> +		 * This rules out writes that need zeroing or extent conversion,
> +		 * extend the file size, or issue metadata I/O or cache flushes
> +		 * during completion processing.
>  		 */
> -		if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
> -		    (dio->flags & IOMAP_DIO_WRITE_THROUGH) &&
> -		    (bdev_fua(iomap->bdev) || !bdev_write_cache(iomap->bdev)))
> -			use_fua = true;
> -		else if (dio->flags & IOMAP_DIO_NEED_SYNC)
> +		if (need_zeroout || (pos >= i_size_read(inode)) ||
> +		    ((dio->flags & IOMAP_DIO_NEED_SYNC) &&
> +		     !(bio_opf & REQ_FUA)))
>  			dio->flags &= ~IOMAP_DIO_CALLER_COMP;
> +	} else {
> +		bio_opf |= REQ_OP_READ;
>  	}
>  
>  	/*
> @@ -399,18 +399,6 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  	if (!iov_iter_count(dio->submit.iter))
>  		goto out;
>  
> -	/*
> -	 * We can only do deferred completion for pure overwrites that
> -	 * don't require additional IO at completion. This rules out
> -	 * writes that need zeroing or extent conversion, extend
> -	 * the file size, or issue journal IO or cache flushes
> -	 * during completion processing.
> -	 */
> -	if (need_zeroout ||
> -	    ((dio->flags & IOMAP_DIO_NEED_SYNC) && !use_fua) ||
> -	    ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
> -		dio->flags &= ~IOMAP_DIO_CALLER_COMP;
> -
>  	/*
>  	 * The rules for polled IO completions follow the guidelines as the
>  	 * ones we set for inline and deferred completions. If none of those
> @@ -428,8 +416,6 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  			goto out;
>  	}
>  
> -	bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua, atomic_hw);
> -
>  	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
>  	do {
>  		size_t n;
> @@ -461,7 +447,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  		}
>  
>  		n = bio->bi_iter.bi_size;
> -		if (WARN_ON_ONCE(atomic_hw && n != length)) {
> +		if (WARN_ON_ONCE((bio_opf & REQ_ATOMIC) && n != length)) {
>  			/*
>  			 * This bio should have covered the complete length,
>  			 * which it doesn't, so error. We may need to zero out
> -- 
> 2.31.1