linux-ext4 - Re: [PATCH 4/6] ext4: remove code related to punching hole from ext4_ext_insert

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Date:	Fri, 2 Dec 2011 09:09:33 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/6] ext4: remove code related to punching hole from ext4_ext_insert_extent

On Fri, Dec 2, 2011 at 4:55 AM, Allison Henderson
<achender@...ux.vnet.ibm.com> wrote:
> On 11/16/2011 07:03 PM, Yongqiang Yang wrote:
>>
>> Punch hole should never call ext4_ext_insert_extent, so this patch
>> removes code related to it from ext4_ext_insert_extent.
>>
>> Signed-off-by: Yongqiang Yang<xiaoqiangnk@...il.com>
>> ---
>>  fs/ext4/extents.c |    2 --
>>  1 files changed, 0 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index 6888d1a..720070d 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -1737,8 +1737,6 @@ int ext4_ext_insert_extent(handle_t *handle, struct
>> inode *inode,
>>         * There is no free space in the found leaf.
>>         * We're gonna add a new leaf in the tree.
>>         */
>> -       if (flag&  EXT4_GET_BLOCKS_PUNCH_OUT_EXT)
>> -               flags = EXT4_MB_USE_ROOT_BLOCKS;
>>        err = ext4_ext_create_new_leaf(handle, inode, flags, path, newext);
>>        if (err)
>>                goto cleanup;
>
> Hi Yongqiang,
>
> Actually I believe it does end up inserting an extent if an extent gets
> split. For example, we punch a hole in the middle of an extent, so we first
> split the extent into three pieces, and remove the middle piece.
>
> Because inserting the extra extents can require extra blocks, the operation
> may temporarily consume blocks. The problem that this causes is that if the
> file system is really full, it can fail with ENOSPC, even though punch hole
> is an operation that is supposed to free blocks.  The above
> EXT4_MB_USE_ROOT_BLOCKS flag was put in so that when we punch holes, we can
> borrow reserved blocks to complete the operation to avoid the ENOSPC
> problem.  I had a script to catch this and added to xfstests (test 256). So
> unless there was a change somewhere that I missed, it does not make sense to
> me to take it out at this point.
Got it.  Thank you for your explanation.

Yongqiang.
>
> Allison Henderson
>
>



-- 
Best Wishes
Yongqiang Yang
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