Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Sat, 2015-08-08 at 12:19 -0400, Martin K. Petersen wrote:
> >>>>> "Mike" == Mike Snitzer <snitzer at redhat.com> writes:
>
> Mike> This will translate to all intermediate layers that might split
> Mike> discards needing to worry about granularity/alignment too
> Mike> (e.g. how dm-thinp will have to care because it must generate
> Mike> discard mappings with associated bios based on how blocks were
> Mike> mapped to thinp).
>
> The fundamental issue here is that alignment and granularity should
> never, ever have been enforced at the top of the stack. Horrendous idea
> from the very beginning.
>
> For the < handful of braindead devices that get confused when you do
> partial or misaligned blocks we should have had a quirk that did any
> range adjusting at the bottom in sd_setup_discard_cmnd().
>
> There's a reason I turned discard_zeroes_data off for UNMAP!
>
> Wrt. the range size I don't have a problem with capping at the 32-bit
> bi_size limit. We probably don't want to send commands much bigger than
> that anyway.
How about below?
commit b8ca440bd77653d4d2bac90b7fd1599e9e0e150a
Author: Ming Lin <ming.l at ssi.samsung.com>
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 set max discard sectors to (1<<31)>>9 to ensure
it doesn't overflow bi_size and hopefully it is of the proper
granularity as long as the granularity is a power of two.
Signed-off-by: Ming Lin <ming.l at ssi.samsung.com>
---
block/blk-lib.c | 47 +++++++++++------------------------------------
1 file changed, 11 insertions(+), 36 deletions(-)
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 7688ee3..4859e4b 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -26,6 +26,13 @@ static void bio_batch_end_io(struct bio *bio, int err)
bio_put(bio);
}
+/*
+ * Ensure that max discard sectors doesn't overflow bi_size and hopefully
+ * it is of the proper granularity as long as the granularity is a power
+ * of two.
+ */
+#define MAX_DISCARD_SECTORS ((1U << 31) >> 9)
+
/**
* blkdev_issue_discard - queue a discard
* @bdev: blockdev to issue discard for
@@ -43,8 +50,6 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
DECLARE_COMPLETION_ONSTACK(wait);
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;
@@ -56,21 +61,6 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
if (!blk_queue_discard(q))
return -EOPNOTSUPP;
- /* 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);
- 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))
return -EOPNOTSUPP;
@@ -84,7 +74,7 @@ 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) {
@@ -92,21 +82,8 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
break;
}
- 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.
- */
+ req_sects = min_t(sector_t, nr_sects, MAX_DISCARD_SECTORS);
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 +143,8 @@ 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;