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Subject: Re: [PATCH] ext4: if zeroout fails fall back to splitting the extent
 node
To:     Theodore Ts'o <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>
CC:     <yukuai3@huawei.com>
References: <YRaNKc2PvM+Eyzmp@mit.edu> <20210813212701.366447-1-tytso@mit.edu>
From:   yangerkun <yangerkun@huawei.com>
Message-ID: <2714202a-872e-aa75-7033-fb06a47b9241@huawei.com>
Date:   Sat, 14 Aug 2021 10:15:11 +0800
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在 2021/8/14 5:27, Theodore Ts'o 写道:
> If the underlying storage device is using thin-provisioning, it's
> possible for a zeroout operation to return ENOSPC.
> 
> Commit df22291ff0fd ("ext4: Retry block allocation if we have free blocks
> left") added logic to retry block allocation since we might get free block
> after we commit a transaction. But the ENOSPC from thin-provisioning
> will confuse ext4, and lead to an infinite loop.
> 
> Since using zeroout instead of splitting the extent node is an
> optimization, if it fails, we might as well fall back to splitting the
> extent node.
> 
> Reported-by: yangerkun <yangerkun@huawei.com>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
> 
> I've run this through my battery of tests, and it doesn't cause any
> regressions.  Yangerkun, can you test this and see if this works for
> you?

Will do it.

> 
>   fs/ext4/extents.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 92ad64b89d9b..501516cadc1b 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3569,7 +3569,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
>   				split_map.m_len - ee_block);
>   			err = ext4_ext_zeroout(inode, &zero_ex1);
>   			if (err)
> -				goto out;
> +				goto fallback;
>   			split_map.m_len = allocated;
>   		}
>   		if (split_map.m_lblk - ee_block + split_map.m_len <
> @@ -3583,7 +3583,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
>   						      ext4_ext_pblock(ex));
>   				err = ext4_ext_zeroout(inode, &zero_ex2);
>   				if (err)
> -					goto out;
> +					goto fallback;
>   			}
>   
>   			split_map.m_len += split_map.m_lblk - ee_block;
> @@ -3592,6 +3592,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
>   		}
>   	}
>   
> +fallback:
>   	err = ext4_split_extent(handle, inode, ppath, &split_map, split_flag,
>   				flags);
>   	if (err > 0)
>