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Date: Fri, 22 Jun 2012 07:44:35 +0900
From: Namjae Jeon <linkinjeon@...il.com>
To: Lukáš Czerner <lczerner@...hat.com>
Cc: Ashish Sangwan <ashishsangwan2@...il.com>,
linux-ext4@...r.kernel.org,
Amit Sahrawat <amit.sahrawat83@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Ted Ts'o" <tytso@....edu>
Subject: Re: Punching hole using fallocate is not removing the uninit extent
from extent tree
Hi Lukas.
Have you reproduced this problem ?
Plz reivew our patch.
Thanks.
2012/6/18, Namjae Jeon <linkinjeon@...il.com>:
> Add in mail loop.
>
> 2012/6/18, Namjae Jeon <linkinjeon@...il.com>:
>> 2012/6/18, Lukáš Czerner <lczerner@...hat.com>:
>>> On Mon, 28 May 2012, Ashish Sangwan wrote:
>>>
>>>> Date: Mon, 28 May 2012 19:38:05 +0530
>>>> From: Ashish Sangwan <ashishsangwan2@...il.com>
>>>> To: linux-ext4@...r.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.
>>
>>> 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.
>>
>>>
>>> Thanks!
>>> -Lukas
>>>
>>>>
>>>> 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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>>>>
>>
>
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