On Tue, Oct 13, 2015 at 10:44:11AM -0700, Ming Lin wrote:
> I just did a quick test with a Samsung 900G NVMe device.
> mkfs.xfs is OK on 4.3-rc5.
>
> What's your device model? I may find a similar one to try.
This is a HGST Ultrastar SN100
Analsys and tentativ fix below:
blktrace for before the commit:
259,0 1 2 0.000002543 2394 G D 0 + 8388607 [mkfs.xfs]
259,0 1 3 0.000008230 2394 I D 0 + 8388607 [mkfs.xfs]
259,0 1 4 0.000031090 207 D D 0 + 8388607 [kworker/1:1H]
259,0 1 5 0.000044869 2394 Q D 8388607 + 8388607 [mkfs.xfs]
259,0 1 6 0.000045992 2394 G D 8388607 + 8388607 [mkfs.xfs]
259,0 1 7 0.000049559 2394 I D 8388607 + 8388607 [mkfs.xfs]
259,0 1 8 0.000061551 207 D D 8388607 + 8388607
[kworker/1:1H]
.. and so on.
blktrace with the commit:
259,0 2 1 0.000000000 1228 Q D 0 + 4194304 [mkfs.xfs]
259,0 2 2 0.000002543 1228 G D 0 + 4194304 [mkfs.xfs]
259,0 2 3 0.000010080 1228 I D 0 + 4194304 [mkfs.xfs]
259,0 2 4 0.000082187 267 D D 0 + 4194304 [kworker/2:1H]
259,0 2 5 0.000224869 1228 Q D 4194304 + 4194304 [mkfs.xfs]
259,0 2 6 0.000225835 1228 G D 4194304 + 4194304 [mkfs.xfs]
259,0 2 7 0.000229457 1228 I D 4194304 + 4194304 [mkfs.xfs]
259,0 2 8 0.000238507 267 D D 4194304 + 4194304
[kworker/2:1H]
So discards are smaller, but better aligned. Now if I tweak a single
line in blk-lib.c to be able to use all of bi_size I get the old I/O
pattern back and everything works fine again:
diff --git a/block/blk-lib.c b/block/blk-lib.c
index bd40292..65b61dc 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t
sector,
break;
}
- req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
+ req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
end_sect = sector + req_sects;
bio->bi_iter.bi_sector = sector;
--
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