Commit 3a0be38c authored by Jens Axboe's avatar Jens Axboe
Browse files

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: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 44842f64

fs/iomap/direct-io.c

+20 −14
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ 
 * Private flags for iomap_dio, must not overlap with the public ones in

 * iomap.h:

 */

#define IOMAP_DIO_WRITE_FUA	(1U << 28)

#define IOMAP_DIO_WRITE_THROUGH	(1U << 28)

#define IOMAP_DIO_NEED_SYNC	(1U << 29)

#define IOMAP_DIO_WRITE		(1U << 30)

#define IOMAP_DIO_DIRTY		(1U << 31)
@@ -219,7 +219,7 @@ static void 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_FUA flag in the dio request.

 * clearing the WRITE_THROUGH flag in the dio request.

 */

static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,

		const struct iomap *iomap, bool use_fua)
@@ -233,7 +233,7 @@ static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio, 
	if (use_fua)

		opflags |= REQ_FUA;

	else

		dio->flags &= ~IOMAP_DIO_WRITE_FUA;

		dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;



	return opflags;

}
@@ -273,11 +273,13 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter, 
		 * 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 supports FUA. This allows us to avoid

		 * cache flushes on IO completion.

		 * 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 (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&

		    (dio->flags & IOMAP_DIO_WRITE_FUA) && bdev_fua(iomap->bdev))

		    (dio->flags & IOMAP_DIO_WRITE_THROUGH) &&

		    (bdev_fua(iomap->bdev) || !bdev_write_cache(iomap->bdev)))

			use_fua = true;

	}
@@ -553,13 +555,16 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
			dio->flags |= IOMAP_DIO_NEED_SYNC;



		       /*

			* For datasync only writes, we optimistically try

			* using FUA for this IO.  Any non-FUA write that

			* occurs will clear this flag, hence we know before

			* completion whether a cache flush is necessary.

			* For datasync only writes, we optimistically try using

			* WRITE_THROUGH for this IO. This flag requires either

			* FUA writes through the device's write cache, or a

			* normal write to a device without a volatile write

			* cache. For the former, Any non-FUA write that occurs

			* will clear this flag, hence we know before completion

			* whether a cache flush is necessary.

			*/

			if (!(iocb->ki_flags & IOCB_SYNC))

				dio->flags |= IOMAP_DIO_WRITE_FUA;

				dio->flags |= IOMAP_DIO_WRITE_THROUGH;

		}



		/*
@@ -621,10 +626,11 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
		iomap_dio_set_error(dio, ret);



	/*

	 * If all the writes we issued were FUA, we don't need to flush the

	 * cache on IO completion. Clear the sync flag for this case.

	 * If all the writes we issued were already written through to the

	 * media, we don't need to flush the cache on IO completion. Clear the

	 * sync flag for this case.

	 */

	if (dio->flags & IOMAP_DIO_WRITE_FUA)

	if (dio->flags & IOMAP_DIO_WRITE_THROUGH)

		dio->flags &= ~IOMAP_DIO_NEED_SYNC;



	WRITE_ONCE(iocb->private, dio->submit.poll_bio);