On 2020/03/25 7:46, Dave Chinner wrote:
> On Wed, Mar 25, 2020 at 12:24:53AM +0900, Johannes Thumshirn wrote:
>> Use REQ_OP_ZONE_APPEND for direct I/O write BIOs, instead of REQ_OP_WRITE
>> if the file-system requests it. The file system can make this request
>> by setting the new flag IOCB_ZONE_APPEND for a direct I/O kiocb before
>> calling iompa_dio_rw(). Using this information, this function propagates
>> the zone append flag using IOMAP_ZONE_APPEND to the file system
>> iomap_begin() method. The BIOs submitted for the zone append DIO will be
>> set to use the REQ_OP_ZONE_APPEND operation.
>>
>> Since zone append operations cannot be split, the iomap_apply() and
>> iomap_dio_rw() internal loops are executed only once, which may result
>> in short writes.
>>
>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
>> ---
>> fs/iomap/direct-io.c | 80 ++++++++++++++++++++++++++++++++++++-------
>> include/linux/fs.h | 1 +
>> include/linux/iomap.h | 22 ++++++------
>> 3 files changed, 79 insertions(+), 24 deletions(-)
>>
>> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
>> index 23837926c0c5..b3e2aadce72f 100644
>> --- a/fs/iomap/direct-io.c
>> +++ b/fs/iomap/direct-io.c
>> @@ -17,6 +17,7 @@
>> * Private flags for iomap_dio, must not overlap with the public ones in
>> * iomap.h:
>> */
>> +#define IOMAP_DIO_ZONE_APPEND (1 << 27)
>> #define IOMAP_DIO_WRITE_FUA (1 << 28)
>> #define IOMAP_DIO_NEED_SYNC (1 << 29)
>> #define IOMAP_DIO_WRITE (1 << 30)
>> @@ -39,6 +40,7 @@ struct iomap_dio {
>> struct task_struct *waiter;
>> struct request_queue *last_queue;
>> blk_qc_t cookie;
>> + sector_t sector;
>> } submit;
>>
>> /* used for aio completion: */
>> @@ -151,6 +153,9 @@ static void iomap_dio_bio_end_io(struct bio *bio)
>> if (bio->bi_status)
>> iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));
>>
>> + if (dio->flags & IOMAP_DIO_ZONE_APPEND)
>> + dio->submit.sector = bio->bi_iter.bi_sector;
>> +
>> if (atomic_dec_and_test(&dio->ref)) {
>> if (dio->wait_for_completion) {
>> struct task_struct *waiter = dio->submit.waiter;
>> @@ -194,6 +199,21 @@ iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
>> iomap_dio_submit_bio(dio, iomap, bio);
>> }
>>
>> +static sector_t
>> +iomap_dio_bio_sector(struct iomap_dio *dio, struct iomap *iomap, loff_t pos)
>> +{
>> + sector_t sector = iomap_sector(iomap, pos);
>> +
>> + /*
>> + * For zone append writes, the BIO needs to point at the start of the
>> + * zone to append to.
>> + */
>> + if (dio->flags & IOMAP_DIO_ZONE_APPEND)
>> + sector = ALIGN_DOWN(sector, bdev_zone_sectors(iomap->bdev));
>> +
>> + return sector;
>> +}
>
> This seems to me like it should be done by the ->iomap_begin
> implementation when mapping the IO. I don't see why this needs to be
> specially handled by the iomap dio code.
Fair point. However, iomap_sector() does not simply return iomap->addr >> 9. So
that means that in iomap_begin, the mapping address and offset returned needs to
account for the iomap_sector() calculation, i.e.
(iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT
which does not result in a very obvious values for iomap address and offset.
Well I guess for zone append we simply need to set
iomap->offset = pos;
and
iomap->addr = zone start sector;
and that would then work. This however look fragile to me.
>
>> +
>> static loff_t
>> iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>> struct iomap_dio *dio, struct iomap *iomap)
>> @@ -204,6 +224,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>> struct bio *bio;
>> bool need_zeroout = false;
>> bool use_fua = false;
>> + bool zone_append = false;
>> int nr_pages, ret = 0;
>> size_t copied = 0;
>> size_t orig_count;
>> @@ -235,6 +256,9 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>> use_fua = true;
>> }
>>
>> + if (dio->flags & IOMAP_DIO_ZONE_APPEND)
>> + zone_append = true;
>> +
>> /*
>> * Save the original count and trim the iter to just the extent we
>> * are operating on right now. The iter will be re-expanded once
>> @@ -266,12 +290,28 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>>
>> bio = bio_alloc(GFP_KERNEL, nr_pages);
>> bio_set_dev(bio, iomap->bdev);
>> - bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
>> + bio->bi_iter.bi_sector = iomap_dio_bio_sector(dio, iomap, pos);
>> bio->bi_write_hint = dio->iocb->ki_hint;
>> bio->bi_ioprio = dio->iocb->ki_ioprio;
>> bio->bi_private = dio;
>> bio->bi_end_io = iomap_dio_bio_end_io;
>>
>> + if (dio->flags & IOMAP_DIO_WRITE) {
>> + bio->bi_opf = REQ_SYNC | REQ_IDLE;
>> + if (zone_append)
>> + bio->bi_opf |= REQ_OP_ZONE_APPEND;
>> + else
>> + bio->bi_opf |= REQ_OP_WRITE;
>> + if (use_fua)
>> + bio->bi_opf |= REQ_FUA;
>> + else
>> + dio->flags &= ~IOMAP_DIO_WRITE_FUA;
>> + } else {
>> + bio->bi_opf = REQ_OP_READ;
>> + if (dio->flags & IOMAP_DIO_DIRTY)
>> + bio_set_pages_dirty(bio);
>> + }
>
> Why move all this code? If it's needed, please split it into a
> separate patchi to separate it from the new functionality...
The BIO add page in bio_iov_iter_get_pages() needs to know that the BIO is a
zone append to stop adding pages before the BIO grows too large and result in a
split when it is submitted. So bio->bi_opf needs to be set before calling
bio_iov_iter_get_pages(). So this change is related to the new functionality.
But I guess it is OK to do it regardless of the BIO operation.
>
>> +
>> ret = bio_iov_iter_get_pages(bio, dio->submit.iter);
>> if (unlikely(ret)) {
>> /*
>> @@ -284,19 +324,10 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>> goto zero_tail;
>> }
>>
>> - n = bio->bi_iter.bi_size;
>> - if (dio->flags & IOMAP_DIO_WRITE) {
>> - bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
>> - if (use_fua)
>> - bio->bi_opf |= REQ_FUA;
>> - else
>> - dio->flags &= ~IOMAP_DIO_WRITE_FUA;
>> + if (dio->flags & IOMAP_DIO_WRITE)
>> task_io_account_write(n);
>> - } else {
>> - bio->bi_opf = REQ_OP_READ;
>> - if (dio->flags & IOMAP_DIO_DIRTY)
>> - bio_set_pages_dirty(bio);
>> - }
>> +
>> + n = bio->bi_iter.bi_size;
>>
>> dio->size += n;
>> pos += n;
>> @@ -304,6 +335,15 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>>
>> nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
>> iomap_dio_submit_bio(dio, iomap, bio);
>> +
>> + /*
>> + * Issuing multiple BIOs for a large zone append write can
>> + * result in reordering of the write fragments and to data
>> + * corruption. So always stop after the first BIO is issued.
>> + */
>> + if (zone_append)
>> + break;
>
> I don't think this sort of functionality should be tied to "zone
> append". If there is a need for "issue a single (short) bio only" it
> should be a flag to iomap_dio_rw() set by the filesystem, which can
> then handle the short read/write that is returned.
Yes, that would be cleaner.
>
>> + /*
>> + * Zone append writes cannot be split and be shorted. Break
>> + * here to let the user know instead of sending more IOs which
>> + * could get reordered and corrupt the written data.
>> + */
>> + if (flags & IOMAP_ZONE_APPEND)
>> + break;
>
> ditto.
>
> Cheers,
>
> Dave.
>
--
Damien Le Moal
Western Digital Research
