On Mon, 28 May 2012, Ashish Sangwan wrote:
> Date: Mon, 28 May 2012 19:38:05 +0530
> From: Ashish Sangwan <ashishsangwan2@xxxxxxxxx>
> To: linux-ext4@xxxxxxxxxxxxxxx
> 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 ?
Also what kernel version did try this on ?
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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