Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
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 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 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 at ssi.samsung.com>
---
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;
>
> Note that this isn't special casing, we can't build > 4GB bios for
> data either, it's just implemented as a side effect right now instead
> of checked explicitly.