How do people think I should implement this functionality? I see
three possible choices:
1) The patch attached below
2) Add this functionality to blk-lib.c, but with a new function name,
such as blkdev_zero_blocks(), and keep blkdev_issue_zeroout()
unchanged
3) This functionality shouldn't be in the block device layer; if you
want something like this, add it to fs/ext4 instead, and other file
systems can optimize sb_issue_zeroout() themselves if they want.
And if the answer is (1) or (2), do people mind if I carry this patch
in the ext4 tree, so I can use and test this right away, without
having to worry about merging with the block tree?
Thanks,
- Ted
commit 1af2359e6ffca707c41ed40618773abe944d0c54
Author: Theodore Ts'o <tytso@xxxxxxx>
Date: Thu Feb 13 23:27:27 2014 -0500
block: use discard if possible in blkdev_issue_zeroout()
If the block device supports discards and guarantees that subsequent
reads will return zeros (sometimes known as DZAT, for Deterministic
read Zeros After Trim), use this to implement blkdev_issue_zeroout()
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2da76c9..62cbf28 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -269,6 +269,32 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
return ret;
}
+static int issue_zeroout_or_write_same(struct block_device *bdev,
+ sector_t sector,
+ sector_t nr_sects, gfp_t gfp_mask)
+{
+ if (bdev_write_same(bdev)) {
+ unsigned char bdn[BDEVNAME_SIZE];
+
+ if (!blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
+ ZERO_PAGE(0)))
+ return 0;
+
+ bdevname(bdev, bdn);
+ pr_err("%s: WRITE SAME failed. Manually zeroing.\n", bdn);
+ }
+
+ return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask);
+}
+
+/*
+ * Like sector_div except don't modify s.
+ */
+static unsigned int sector_mod(sector_t s, unsigned int m)
+{
+ return sector_div(s, m);
+}
+
/**
* blkdev_issue_zeroout - zero-fill a block range
* @bdev: blockdev to write
@@ -277,23 +303,49 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
* @gfp_mask: memory allocation flags (for bio_alloc)
*
* Description:
- * Generate and issue number of bios with zerofiled pages.
+ * Issues bios which zeros the requested block range.
*/
-
int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
sector_t nr_sects, gfp_t gfp_mask)
{
- if (bdev_write_same(bdev)) {
- unsigned char bdn[BDEVNAME_SIZE];
+ struct request_queue *q = bdev_get_queue(bdev);
+ unsigned int alignment, granularity;
+ unsigned int c;
+ int ret;
- if (!blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
- ZERO_PAGE(0)))
- return 0;
+ if (!q)
+ return -ENXIO;
- bdevname(bdev, bdn);
- pr_err("%s: WRITE SAME failed. Manually zeroing.\n", bdn);
+ if (!blk_queue_discard(q) || !queue_discard_zeroes_data(q) ||
+ q->limits.discard_misaligned)
+ return issue_zeroout_or_write_same(bdev, sector,
+
+ nr_sects, gfp_mask);
+
+ alignment = q->limits.discard_alignment >> 9;
+ granularity = q->limits.discard_granularity >> 9;
+
+ c = sector_mod(granularity + alignment - sector, granularity);
+ if (c > nr_sects)
+ c = nr_sects;
+
+ if (c) {
+ int ret = issue_zeroout_or_write_same(bdev, sector,
+ c, gfp_mask);
+ if (ret)
+ return ret;
+ nr_sects -= c;
}
+ if (nr_sects == 0)
+ return 0;
- return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask);
+ c = sector_mod(nr_sects, granularity);
+
+ ret = blkdev_issue_discard(bdev, sector, nr_sects - c, gfp_mask, 0);
+ if (ret || c == 0)
+ return ret;
+
+ return issue_zeroout_or_write_same(bdev, sector + nr_sects - c, c,
+ gfp_mask);
}
EXPORT_SYMBOL(blkdev_issue_zeroout);
--
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