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Message-ID: <87cyeh5c21.fsf@gmail.com>
Date: Sun, 16 Mar 2025 19:10:06 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, brauner@...nel.org, djwong@...nel.org, cem@...nel.org, dchinner@...hat.com, hch@....de
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com, martin.petersen@...cle.com, tytso@....edu, linux-ext4@...r.kernel.org, John Garry <john.g.garry@...cle.com>
Subject: Re: [PATCH v6 01/13] iomap: inline iomap_dio_bio_opflags()
John Garry <john.g.garry@...cle.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@...il.com>
> Originally-from: Christoph Hellwig <hch@....de>
> Signed-off-by: John Garry <john.g.garry@...cle.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
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