When yangerkun review commit 93cdf49f6eca ("ext4: Fix best extent lstart
adjustment logic in ext4_mb_new_inode_pa()"), it was found that the best
extent did not completely cover the original request after adjusting the
best extent lstart in ext4_mb_new_inode_pa() as follows:
original request: 2/10(8)
normalized request: 0/64(64)
best extent: 0/9(9)
When we check if best ex can be kept at start of goal, ac_o_ex.fe_logical
is 2 less than the adjusted best extent logical end 9, so we think the
adjustment is done. But obviously 0/9(9) doesn't cover 2/10(8), so we
should determine here if the original request logical end is less than or
equal to the adjusted best extent logical end.
In addition, add a comment stating when adjusted best_ex will not cover
the original request, and remove the duplicate assertion because adjusting
lstart makes no change to b_ex.fe_len.
Link: https://lore.kernel.org/r/3630fa7f-b432-7afd-5f79-781bc3b2c5ea@xxxxxxxxxx
Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
Cc: stable@xxxxxxxxxx
Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
V1->V2:
Remove the problematic BUG_ON and add some comments.
fs/ext4/mballoc.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 1ea6491b6b00..20cad0676aab 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -5148,10 +5148,16 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
.fe_len = ac->ac_orig_goal_len,
};
loff_t orig_goal_end = extent_logical_end(sbi, &ex);
+ loff_t o_ex_end = extent_logical_end(sbi, &ac->ac_o_ex);
- /* we can't allocate as much as normalizer wants.
- * so, found space must get proper lstart
- * to cover original request */
+ /*
+ * We can't allocate as much as normalizer wants, so we try
+ * to get proper lstart to cover the original request, except
+ * when the goal doesn't cover the original request as below:
+ *
+ * orig_ex:2045/2055(10), isize:8417280 -> normalized:0/2048
+ * best_ex:0/200(200) -> adjusted: 1848/2048(200)
+ */
BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);
@@ -5163,7 +5169,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
* 1. Check if best ex can be kept at end of goal (before
* cr_best_avail trimmed it) and still cover original start
* 2. Else, check if best ex can be kept at start of goal and
- * still cover original start
+ * still cover original end
* 3. Else, keep the best ex at start of original request.
*/
ex.fe_len = ac->ac_b_ex.fe_len;
@@ -5173,7 +5179,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
goto adjust_bex;
ex.fe_logical = ac->ac_g_ex.fe_logical;
- if (ac->ac_o_ex.fe_logical < extent_logical_end(sbi, &ex))
+ if (o_ex_end <= extent_logical_end(sbi, &ex))
goto adjust_bex;
ex.fe_logical = ac->ac_o_ex.fe_logical;
@@ -5181,7 +5187,6 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
ac->ac_b_ex.fe_logical = ex.fe_logical;
BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
- BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
BUG_ON(extent_logical_end(sbi, &ex) > orig_goal_end);
}
--
2.31.1
