[PATCH] ext4: merge uninitialized extents

[Ming Lei]

Hi,

On Wed, Mar 11, 2015 at 5:03 PM, Stefan Bader
<stefan.bader at canonical.com> wrote:
> On 11.03.2015 04:50, Ming Lei wrote:
>> From: "Darrick J. Wong" <darrick.wong at oracle.com>
>>
>> Buglink:
>>         https://bugs.launchpad.net/bugs/1430184
>>
>> Upstream commit:
>>         a9b8241 ext4: merge uninitialized extents
>
> Hi Ming,
>
> it would help to add here whether the patch could be cherry-picked or needed
> some backporting. From the look of it, it seems to be a clean pick.

Yes, 'git am' can apply the patch cleanly.

> Oh and also it helps to know what release(s) are targeted from the subject of an
> SRU email. In this case it has to be Trusty according to the comments in the bug
> report and the fact this patch came with 3.15.
>
> Generally I am a bit undecided about this one. The commit message does not
> really sound like this was considered a fix for something misbehaving. And the
> fact that xfs tests fail may also be due to the test-case not properly checking
> the features available. So the question for me would be whether there is a real
> world use-case broken or not.

The xfstest tests(generic/324 and ext4/308) doesn't depend on
some 'features'.

This test just makes some holes in one file over ext4 via falloc & write,
then run 'e4defrag' to try to reduce fragmentation of the file.

Unfortunately the fragmentation of the test file aren't reduced by
e4defrag on trusty in this test case , instead of being increased
a lot(for 36 to 500+), so the bug can affect performance.

Please see the 1st sentence in DESCRIPTION section of man page
of e4defrag:

     'e4defrag  reduces fragmentation of extent based file.'

Thanks,
Ming Lei

>
> -Stefan
>
>>
>> Allow for merging uninitialized extents.
>>
>> Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
>> Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
>> ---
>>  fs/ext4/extents.c |   21 +++++++++++++++++----
>>  1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index 9875fd0..ef4b535 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -1691,7 +1691,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
>>        * the extent that was written properly split out and conversion to
>>        * initialized is trivial.
>>        */
>> -     if (ext4_ext_is_uninitialized(ex1) || ext4_ext_is_uninitialized(ex2))
>> +     if (ext4_ext_is_uninitialized(ex1) != ext4_ext_is_uninitialized(ex2))
>>               return 0;
>>
>>       ext1_ee_len = ext4_ext_get_actual_len(ex1);
>> @@ -1708,6 +1708,11 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
>>        */
>>       if (ext1_ee_len + ext2_ee_len > EXT_INIT_MAX_LEN)
>>               return 0;
>> +     if (ext4_ext_is_uninitialized(ex1) &&
>> +         (ext4_test_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN) ||
>> +          atomic_read(&EXT4_I(inode)->i_unwritten) ||
>> +          (ext1_ee_len + ext2_ee_len > EXT_UNINIT_MAX_LEN)))
>> +             return 0;
>>  #ifdef AGGRESSIVE_TEST
>>       if (ext1_ee_len >= 4)
>>               return 0;
>> @@ -1731,7 +1736,7 @@ static int ext4_ext_try_to_merge_right(struct inode *inode,
>>  {
>>       struct ext4_extent_header *eh;
>>       unsigned int depth, len;
>> -     int merge_done = 0;
>> +     int merge_done = 0, uninit;
>>
>>       depth = ext_depth(inode);
>>       BUG_ON(path[depth].p_hdr == NULL);
>> @@ -1741,8 +1746,11 @@ static int ext4_ext_try_to_merge_right(struct inode *inode,
>>               if (!ext4_can_extents_be_merged(inode, ex, ex + 1))
>>                       break;
>>               /* merge with next extent! */
>> +             uninit = ext4_ext_is_uninitialized(ex);
>>               ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
>>                               + ext4_ext_get_actual_len(ex + 1));
>> +             if (uninit)
>> +                     ext4_ext_mark_uninitialized(ex);
>>
>>               if (ex + 1 < EXT_LAST_EXTENT(eh)) {
>>                       len = (EXT_LAST_EXTENT(eh) - ex - 1)
>> @@ -1896,7 +1904,7 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
>>       struct ext4_ext_path *npath = NULL;
>>       int depth, len, err;
>>       ext4_lblk_t next;
>> -     int mb_flags = 0;
>> +     int mb_flags = 0, uninit;
>>
>>       if (unlikely(ext4_ext_get_actual_len(newext) == 0)) {
>>               EXT4_ERROR_INODE(inode, "ext4_ext_get_actual_len(newext) == 0");
>> @@ -1946,9 +1954,11 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
>>                                                 path + depth);
>>                       if (err)
>>                               return err;
>> -
>> +                     uninit = ext4_ext_is_uninitialized(ex);
>>                       ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
>>                                       + ext4_ext_get_actual_len(newext));
>> +                     if (uninit)
>> +                             ext4_ext_mark_uninitialized(ex);
>>                       eh = path[depth].p_hdr;
>>                       nearex = ex;
>>                       goto merge;
>> @@ -1971,10 +1981,13 @@ prepend:
>>                       if (err)
>>                               return err;
>>
>> +                     uninit = ext4_ext_is_uninitialized(ex);
>>                       ex->ee_block = newext->ee_block;
>>                       ext4_ext_store_pblock(ex, ext4_ext_pblock(newext));
>>                       ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
>>                                       + ext4_ext_get_actual_len(newext));
>> +                     if (uninit)
>> +                             ext4_ext_mark_uninitialized(ex);
>>                       eh = path[depth].p_hdr;
>>                       nearex = ex;
>>                       goto merge;
>>
>
>