On 08/08/2015 01:40 AM, Ming Lin wrote:
>
> On Fri, 2015-08-07 at 09:30 +0200, Christoph Hellwig wrote:
>> I'm for solution 3:
>>
>> - keep blk_bio_{discard,write_same}_split, but ensure we never built
>> a > 4GB bio in blkdev_issue_{discard,write_same}.
>
> This has problem as I mentioned in solution 1.
> We need to also make sure max discard size is of proper granularity.
> See below example.
>
> 4G: 8388608 sectors
> UINT_MAX: 8388607 sectors
>
> dm-thinp block size = default discard granularity = 128 sectors
>
> blkdev_issue_discard(sector=0, nr_sectors=8388608)
>
> 1. Only ensure bi_size not overflow
>
> It doesn't work.
>
> [start_sector, end_sector]
> [0, 8388607]
> [0, 8388606], then dm-thinp splits it to 2 bios
> [0, 8388479]
> [8388480, 8388606] ---> this has problem in process_discard_bio(),
> because the discard size(7 sectors) covers less than a block(128 sectors)
> [8388607, 8388607] ---> same problem
>
> 2. Ensure bi_size not overflow and max discard size is of proper granularity
>
> It works.
>
> [start_sector, end_sector]
> [0, 8388607]
> [0, 8388479]
> [8388480, 8388607]
>
>
> So how about below patch?
>
> commit 1ca2ad977255efb3c339f4ca16fb798ed5ec54f7
> Author: Ming Lin <ming.l@xxxxxxxxxxxxxxx>
> Date: Fri Aug 7 15:07:07 2015 -0700
>
> block: remove split code in blkdev_issue_{discard,write_same}
>
> The split code in blkdev_issue_{discard,write_same} can go away
> now that any driver that cares does the split. We have to make
> sure bio size doesn't overflow.
>
> For discard, we ensure max_discard_sectors is of the proper
> granularity. So if discard size > 4G, blkdev_issue_discard() always
> send multiple granularity requests to lower level, except that the
> last one may be not multiple granularity.
>
> Signed-off-by: Ming Lin <ming.l@xxxxxxxxxxxxxxx>
> ---
> block/blk-lib.c | 37 +++++++++----------------------------
> 1 file changed, 9 insertions(+), 28 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 7688ee3..e178a07 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -44,7 +44,6 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> struct request_queue *q = bdev_get_queue(bdev);
> int type = REQ_WRITE | REQ_DISCARD;
> unsigned int max_discard_sectors, granularity;
> - int alignment;
> struct bio_batch bb;
> struct bio *bio;
> int ret = 0;
> @@ -58,18 +57,15 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>
> /* Zero-sector (unknown) and one-sector granularities are the same. */
> granularity = max(q->limits.discard_granularity >> 9, 1U);
> - alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
>
> /*
> - * Ensure that max_discard_sectors is of the proper
> - * granularity, so that requests stay aligned after a split.
> - */
> - max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
> + * Ensure that max_discard_sectors doesn't overflow bi_size and is of
> + * the proper granularity. So if discard size > 4G, blkdev_issue_discard()
> + * always split and send multiple granularity requests to lower level,
> + * except that the last one may be not multiple granularity.
> + */
> + max_discard_sectors = UINT_MAX >> 9;
> max_discard_sectors -= max_discard_sectors % granularity;
> - if (unlikely(!max_discard_sectors)) {
> - /* Avoid infinite loop below. Being cautious never hurts. */
> - return -EOPNOTSUPP;
> - }
>
> if (flags & BLKDEV_DISCARD_SECURE) {
> if (!blk_queue_secdiscard(q))
> @@ -84,7 +80,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> blk_start_plug(&plug);
> while (nr_sects) {
> unsigned int req_sects;
> - sector_t end_sect, tmp;
> + sector_t end_sect;
>
> bio = bio_alloc(gfp_mask, 1);
> if (!bio) {
> @@ -93,20 +89,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> }
>
> req_sects = min_t(sector_t, nr_sects, max_discard_sectors);
> -
> - /*
> - * If splitting a request, and the next starting sector would be
> - * misaligned, stop the discard at the previous aligned sector.
> - */
> end_sect = sector + req_sects;
> - tmp = end_sect;
> - if (req_sects < nr_sects &&
> - sector_div(tmp, granularity) != alignment) {
> - end_sect = end_sect - alignment;
> - sector_div(end_sect, granularity);
> - end_sect = end_sect * granularity + alignment;
> - req_sects = end_sect - sector;
> - }
>
> bio->bi_iter.bi_sector = sector;
> bio->bi_end_io = bio_batch_end_io;
> @@ -166,10 +149,8 @@ int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
> if (!q)
> return -ENXIO;
>
> - max_write_same_sectors = q->limits.max_write_same_sectors;
> -
> - if (max_write_same_sectors == 0)
> - return -EOPNOTSUPP;
> + /* Ensure that max_write_same_sectors doesn't overflow bi_size */
> + max_write_same_sectors = UINT_MAX >> 9;
>
> atomic_set(&bb.done, 1);
> bb.flags = 1 << BIO_UPTODATE;
>
Wouldn't it be easier to move both max_write_same_sectors and
max_discard sectors to 64 bit (ie to type sector_t) and be done with the
overflow?
Seems to me this is far too much coding around self-imposed restrictions...
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
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SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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