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@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- fs/iomap/direct-io.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index 7d627d43d10b..6b690fc22365 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -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); -- 2.40.1
