Hi Lukas.

Have you reproduced this problem ?
Plz reivew our patch.

Thanks.

2012/6/18, Namjae Jeon [off-list ref]:

Add in mail loop.

2012/6/18, Namjae Jeon [off-list ref]:

quoted

2012/6/18, Lukáš Czerner [off-list ref]:

quoted

On Mon, 28 May 2012, Ashish Sangwan wrote:

quoted

Date: Mon, 28 May 2012 19:38:05 +0530
From: Ashish Sangwan <redacted>
To: linux-ext4@vger.kernel.org
Subject: Punching hole using fallocate is not removing the uninit
extent
from
    extent tree

Hi Ashish,

I am looking at you patch, however I am not able to reproduce this.
Can you please send more information (script preferably) on how to
reproduce this problem ?

Hi. Lukas.
If you use the below script, you can easily reproduce this problem.
And I can not attach script file, so I write script code in this mail.
you can paste it to file.

fragmentation.sh
-----------------------------------------------------------------------
dd if=/dev/zero of=12kb bs=4096 count=6
index=0
while [ $? == 0 ]
do
index=$(($index + 1))
cp 12kb $1/file1.$index
done
echo "Partition filled"
sync
df -h
index=0
while [ $? == 0 ]
do
index=$(($index + 2))
sync
rm  $1/file1.$index
done
sync
echo "fragmented partition $1 with 4KB files"
-------------------------------------------------------------------------

1. create smaill partition(500MB) to reproduce rapidly.
2. plz run this script to make fragmentation partition after making
dummy directory like this.
mkdir test_dir
./fragmentation.sh test_dir

3. dd if=/dev/zero of=d_file bs=1024 count=10240
4. you can see file depth is not zero.(dump_extents d_file
5. and try to fallocate offset : 4096 lengh 4096.

quoted

Also what kernel version did try this on ?

We are using 3.0.20 kernel patched your punch hole patches.

Please let us know in case of any queries.

Thanks.

quoted

Thanks!
-Lukas

quoted

I have created a formatted EXT4 partition such that every single
extent is exactly 6blocks (24KB) of length.
I used hole punch on 2 different files.

CASE 1: In first situation, file size is 72KB. There are total 3
extents each 24KB length. Using fallocate to punch hole starting at
offset 4096 and length 4096,
dump_extents gives the following expected output :

Before punching hole :
Level Entries       Logical      Physical Length Flags
0/ 0   1/  2     0 -     5  1856 -  1861      6
0/ 0   2/  2     6 -    11  1868 -  1873      6

After punching hole :
Level Entries       Logical      Physical Length Flags
0/ 0   1/  3     0 -     0  1856 -  1856      1
0/ 0   2/  3     2 -     5  1858 -  1861      4
0/ 0   3/  3     6 -    11  1868 -  1873      6

The 1st extent: 0-5, is splitted into 3 extents, "0-0", "1-1", "2-5"
Extent 1-1 is first marked as uninitialized in function
ext4_ext_map_blocks() and later removed from the extent tree by
ext4_ext_remove_space().

CASE 2: File size is 9.4MB. There are total 400 extents each 24KB
length, depth of extent tree at root header is 1 and there are 2 index
entries.

dump_extents output before punching hole:
Level Entries       Logical      Physical Length Flags
0/ 1   1/  2     0 -  2039  1922           2040
1/ 1   1/340     0 -     5  1856 -  1861      6
1/ 1   2/340     6 -    11  1868 -  1873      6
< Continued likewise till 340/340 >
1/ 1 340/340  2034 -  2039  5942 -  5947      6
0/ 1   2/  2  2040 -  2399  1923            360
1/ 1   1/ 60  2040 -  2045  5954 -  5959      6
1/ 1   2/ 60  2046 -  2051  5966 -  5971      6
< Continued likewise till 60/60 >
1/ 1  60/ 60  2394 -  2399  6662 -  6667      6

dump_extents output after punching hole :
0/ 1   1/  3     0 -     5  1922              6
1/ 1   1/  3     0 -     0  1856 -  1856      1
1/ 1   2/  3     1 -     1  1857 -  1857      1 Uninit
1/ 1   3/  3     2 -     5  1858 -  1861      4
0/ 1   2/  3     6 -  2039  6674           2034
1/ 1   1/339     6 -    11  1868 -  1873      6
1/ 1   2/339    12 -    17  1880 -  1885      6
< Continued like wise...>

Comparing CASE2 with CASE1, still uninit extent "1-1" is present
within the extent tree.

In function ext4_ext_remove_space(), there is call to function
ext4_ext_rm_leaf which is responsible for removal of this extent.
But this function is not getting called in CASE 2 :
if (i == depth) {
                       /* this is leaf block */
                       err = ext4_ext_rm_leaf(handle, inode, path,
                                       start, end);
/* root level has p_bh == NULL, brelse() eats this */
                       brelse(path[i].p_bh);
                       path[i].p_bh = NULL;
                       i--;
                       continue;
               }

Varibale "i" does not become equals to "depth" because
ext4_ext_more_to_rm is returning "0" hence the following if condition
is turning out to be false for 1st extent index:
if (ext4_ext_more_to_rm(path + i)) {

Looking at the defination of ext4_ext_more_to_rm :
/*
* ext4_ext_more_to_rm:
* returns 1 if current index has to be freed (even partial)
*/
static int
ext4_ext_more_to_rm(struct ext4_ext_path *path)
{
       BUG_ON(path->p_idx == NULL);
       if (path->p_idx < EXT_FIRST_INDEX(path->p_hdr))
               return 0;

       /*
        * if truncate on deeper level happened, it wasn't partial,
        * so we have to consider current index for truncation
        */
       if (le16_to_cpu(path->p_hdr->eh_entries) == path->p_block) <=
This condition is turning out to be true
               return 0;       <= The function is returning zero from
here.
       return 1;
}

I could not understand the significance of the above mentioned if
condition check, if anyone could explain a little, it will be help.
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