On Wed, Oct 14 2015 at 9:27am -0400, Christoph Hellwig <[email protected]> wrote:
> 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; Can we change UINT_MAX >> 9 to rounddown to the first factor of minimum_io_size? That should work for all devices and for dm-thinp (and dm-cache) in particular will ensure that all discards that are issued will be a multiple of the underlying device's blocksize. Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
