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Date: Mon, 18 Jun 2012 20:40:55 +0900
From: Namjae Jeon <linkinjeon@...il.com>
To: Lukáš Czerner <lczerner@...hat.com>
Cc: Ashish Sangwan <ashishsangwan2@...il.com>,
linux-ext4@...r.kernel.org
Subject: Re: Punching hole using fallocate is not removing the uninit extent
from extent tree
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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