linux-ext4 - [PATCH] ext4: fix inconsistent between segment fstrim and full fstrim

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Date: Thu, 14 Dec 2023 14:46:35 +0800
From: Ye Bin <yebin10@...wei.com>
To: <tytso@....edu>, <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <jack@...e.cz>, Ye Bin
	<yebin10@...wei.com>
Subject: [PATCH] ext4: fix inconsistent between segment fstrim and full fstrim

There will not issue discard cmd when do segment fstrim for ext4 fs, however,
if full fstrim for the same fs will issue discard cmd.
Above issue may happens as follows:
Precondition:
1. Fstrim range [0, 15] and [16, 31];
2. Discard granularity is 16;
            Range1          Range2
      1111000000000000 0000111010101011
There's no free space length large or equal than 16 in 'Range1' or 'Range2'.
As ext4_try_to_trim_range() only search free space among range which user
specified. However, there's maximum free space length 16 in 'Range1'+ 'Range2'.
To solve above issue, we need to find the longest free space to discard.

Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 fs/ext4/mballoc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d72b5e3c92ec..d195461123d8 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -6753,13 +6753,15 @@ static int ext4_try_to_trim_range(struct super_block *sb,
 __acquires(ext4_group_lock_ptr(sb, e4b->bd_group))
 __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
 {
-	ext4_grpblk_t next, count, free_count;
+	ext4_grpblk_t next, count, free_count, last, origin_start;
 	bool set_trimmed = false;
 	void *bitmap;
 
+	last = ext4_last_grp_cluster(sb, e4b->bd_group);
 	bitmap = e4b->bd_bitmap;
-	if (start == 0 && max >= ext4_last_grp_cluster(sb, e4b->bd_group))
+	if (start == 0 && max >= last)
 		set_trimmed = true;
+	origin_start = start;
 	start = max(e4b->bd_info->bb_first_free, start);
 	count = 0;
 	free_count = 0;
@@ -6768,7 +6770,10 @@ __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
 		start = mb_find_next_zero_bit(bitmap, max + 1, start);
 		if (start > max)
 			break;
-		next = mb_find_next_bit(bitmap, max + 1, start);
+
+		next = mb_find_next_bit(bitmap, last + 1, start);
+		if (origin_start == 0 && next >= last)
+			set_trimmed = true;
 
 		if ((next - start) >= minblocks) {
 			int ret = ext4_trim_extent(sb, start, next - start, e4b);
-- 
2.31.1