Re: [PATCH V3 2/5] ext4: add new helper interface ext4_try_to_trim_range()

On 2021/8/13 1:44 AM, Theodore Ts'o wrote:

On Sat, Jul 24, 2021 at 03:41:21PM +0800, Wang Jianchao wrote:

quoted

From: Wang Jianchao <redacted>

There is no functional change in this patch but just split the
codes, which serachs free block and does trim, into a new function
ext4_try_to_trim_range. This is preparing for the following async
backgroup discard.

Reviewed-by: Andreas Dilger <redacted>
Signed-off-by: Wang Jianchao <redacted>
---
 fs/ext4/mballoc.c | 102 ++++++++++++++++++++++++++--------------------
 1 file changed, 57 insertions(+), 45 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 018d5d3c6eeb..e3844152a643 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c

@@ -6218,6 +6218,54 @@ __acquires(bitlock)
 	return ret;
 }
 
+static int ext4_try_to_trim_range(struct super_block *sb,
+		struct ext4_buddy *e4b, ext4_grpblk_t start,
+		ext4_grpblk_t max, ext4_grpblk_t minblocks)
+{
+	ext4_grpblk_t next, count, free_count;
+	void *bitmap;
+	int ret = 0;
+
+	bitmap = e4b->bd_bitmap;
+	start = (e4b->bd_info->bb_first_free > start) ?
+		e4b->bd_info->bb_first_free : start;
+	count = 0;
+	free_count = 0;
+
+	while (start <= max) {
+		start = mb_find_next_zero_bit(bitmap, max + 1, start);
+		if (start > max)
+			break;
+		next = mb_find_next_bit(bitmap, max + 1, start);
+
+		if ((next - start) >= minblocks) {
+			ret = ext4_trim_extent(sb, start, next - start, e4b);
+			if (ret && ret != -EOPNOTSUPP)
+				break;
+			ret = 0;
+			count += next - start;
+		}

"ret" is only used inside the if statement, so this might be better as:

quoted

+		if ((next - start) >= minblocks) {
+			int ret = ext4_trim_extent(sb, start, next - start, e4b);
+
+			if (ret && ret != -EOPNOTSUPP)
+				break;
+			count += next - start;
+		}

... and then drop the "int ret = 0" above.

Otherwise, looks good.

OK, I'll do it in next version

Thanks so much
Jianchao

						- Ted