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iomap: treat a write through cache the same as FUA
Whether we have a write back cache and are using FUA or don't have a write back cache at all is the same situation. Treat them the same. This makes the IOMAP_DIO_WRITE_FUA name a bit misleading, as we have two cases that provide stable writes: 1) Volatile write cache with FUA writes 2) Normal write without a volatile write cache Rename that flag to IOMAP_DIO_STABLE_WRITE to make that clearer, and update some of the FUA comments as well. Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -20,7 +20,7 @@
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* Private flags for iomap_dio, must not overlap with the public ones in
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* iomap.h:
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*/
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#define IOMAP_DIO_WRITE_FUA (1U << 28)
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#define IOMAP_DIO_WRITE_THROUGH (1U << 28)
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#define IOMAP_DIO_NEED_SYNC (1U << 29)
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#define IOMAP_DIO_WRITE (1U << 30)
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#define IOMAP_DIO_DIRTY (1U << 31)
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@ -219,7 +219,7 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
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/*
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* Figure out the bio's operation flags from the dio request, the
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* mapping, and whether or not we want FUA. Note that we can end up
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* clearing the WRITE_FUA flag in the dio request.
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* clearing the WRITE_THROUGH flag in the dio request.
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*/
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static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
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const struct iomap *iomap, bool use_fua)
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@ -233,7 +233,7 @@ static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
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if (use_fua)
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opflags |= REQ_FUA;
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else
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dio->flags &= ~IOMAP_DIO_WRITE_FUA;
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dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
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return opflags;
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}
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@ -273,11 +273,13 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
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* Use a FUA write if we need datasync semantics, this is a pure
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* data IO that doesn't require any metadata updates (including
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* after IO completion such as unwritten extent conversion) and
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* the underlying device supports FUA. This allows us to avoid
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* cache flushes on IO completion.
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* the underlying device either supports FUA or doesn't have
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* a volatile write cache. This allows us to avoid cache flushes
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* on IO completion.
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*/
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if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
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(dio->flags & IOMAP_DIO_WRITE_FUA) && bdev_fua(iomap->bdev))
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(dio->flags & IOMAP_DIO_WRITE_THROUGH) &&
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(bdev_fua(iomap->bdev) || !bdev_write_cache(iomap->bdev)))
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use_fua = true;
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}
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@ -553,13 +555,16 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
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dio->flags |= IOMAP_DIO_NEED_SYNC;
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/*
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* For datasync only writes, we optimistically try
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* using FUA for this IO. Any non-FUA write that
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* occurs will clear this flag, hence we know before
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* completion whether a cache flush is necessary.
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* For datasync only writes, we optimistically try using
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* WRITE_THROUGH for this IO. This flag requires either
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* FUA writes through the device's write cache, or a
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* normal write to a device without a volatile write
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* cache. For the former, Any non-FUA write that occurs
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* will clear this flag, hence we know before completion
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* whether a cache flush is necessary.
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*/
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if (!(iocb->ki_flags & IOCB_SYNC))
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dio->flags |= IOMAP_DIO_WRITE_FUA;
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dio->flags |= IOMAP_DIO_WRITE_THROUGH;
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}
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/*
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@ -621,10 +626,11 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
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iomap_dio_set_error(dio, ret);
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/*
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* If all the writes we issued were FUA, we don't need to flush the
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* cache on IO completion. Clear the sync flag for this case.
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* If all the writes we issued were already written through to the
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* media, we don't need to flush the cache on IO completion. Clear the
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* sync flag for this case.
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*/
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if (dio->flags & IOMAP_DIO_WRITE_FUA)
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if (dio->flags & IOMAP_DIO_WRITE_THROUGH)
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dio->flags &= ~IOMAP_DIO_NEED_SYNC;
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WRITE_ONCE(iocb->private, dio->submit.poll_bio);
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