On Sat, 23 Aug 2014 15:08:35 -0400, "Theodore Ts'o" <tytso@xxxxxxx> wrote:
> On Fri, Aug 22, 2014 at 03:32:25PM +0400, Dmitry Monakhov wrote:
> > - handle = ext4_journal_start(inode, EXT4_HT_MISC, 4);
> > + /* In worst case we have to writeout two nonadjacent unwritten blocks */
> > + credits = ext4_chunk_trans_blocks(inode, 1) * 2 -
> > + EXT4_META_TRANS_BLOCKS(inode->i_sb);
>
> This looks like it would be a massive over-estimate, since it includes
> the block group allocation bitmaps, which we wouldn't need to update,
> no?
Oh. You right. groups metadata/quota should not be affected.
>
> Wouldn't
>
> credts = ext4_index_trans_blocks(inode, 1, 1) * 2;
Yes, but ext4_index_trans_blocks is statically defined in inode.c,
but since zero_range works only for extent based
ext4_ext_index_trans_blocks is sufficient. Also we must reserve 2 block
for data. So final calculation looks like follows:
credits = ext4_ext_index_trans_blocks(inode, 2) + 2
>From ec7e1926e8bb99ccd0eb525efc6666cb8ea36a5e Mon Sep 17 00:00:00 2001
From: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
Date: Mon, 25 Aug 2014 11:12:35 +0400
Subject: [PATCH] ext4_zero_range: fix incorect journal credits reservation v2
Currently we reserve only 4 blocks but in worst case scenario
ext4_zero_partial_blocks() may want to zeroout and convert two
non adjacent blocks.
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/extents.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 5bf718b..f09dbe7 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4740,6 +4740,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
loff_t new_size = 0;
int ret = 0;
int flags;
+ int credits;
int partial;
loff_t start, end;
ext4_lblk_t lblk;
@@ -4839,8 +4840,9 @@ static long ext4_zero_range(struct file *file, loff_t offset,
if (ret)
goto out_dio;
}
-
- handle = ext4_journal_start(inode, EXT4_HT_MISC, 4);
+ /* In worst case we have to writeout two nonadjacent unwritten blocks */
+ credits = ext4_ext_index_trans_blocks(inode, 2) + 2;
+ handle = ext4_journal_start(inode, EXT4_HT_MISC, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
ext4_std_error(inode->i_sb, ret);
--
1.7.1
