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Message-ID: <5A1D1A4A.8040506@huawei.com>
Date: Tue, 28 Nov 2017 16:11:54 +0800
From: alex chen <alex.chen@...wei.com>
To: Gang He <ghe@...e.com>
CC: <jlbec@...lplan.org>, <hch@....de>, <ocfs2-devel@....oracle.com>,
"Goldwyn Rodrigues" <RGoldwyn@...e.com>, <mfasheh@...sity.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH 2/3] ocfs2: add ocfs2_overwrite_io function
Hi Gang,
On 2017/11/28 15:38, Gang He wrote:
> Hi Alex,
>
>
>>>>
>> Hi Gang,
>>
>> On 2017/11/28 13:33, Gang He wrote:
>>> Hello Alex,
>>>
>>>
>>>>>>
>>>> Hi Gang,
>>>>
>>>> On 2017/11/27 17:46, Gang He wrote:
>>>>> Add ocfs2_overwrite_io function, which is used to judge if
>>>>> overwrite allocated blocks, otherwise, the write will bring extra
>>>>> block allocation overhead.
>>>>>
>>>>> Signed-off-by: Gang He <ghe@...e.com>
>>>>> ---
>>>>> fs/ocfs2/extent_map.c | 67
>>>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>> fs/ocfs2/extent_map.h | 3 +++
>>>>> 2 files changed, 70 insertions(+)
>>>>>
>>>>> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
>>>>> index e4719e0..98bf325 100644
>>>>> --- a/fs/ocfs2/extent_map.c
>>>>> +++ b/fs/ocfs2/extent_map.c
>>>>> @@ -832,6 +832,73 @@ int ocfs2_fiemap(struct inode *inode, struct
>>>> fiemap_extent_info *fieinfo,
>>>>> return ret;
>>>>> }
>>>>>
>>>>> +/* Is IO overwriting allocated blocks? */
>>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
>>>>> + int wait)
>>>>> +{
>>>>> + int ret = 0, is_last;
>>>>> + u32 mapping_end, cpos;
>>>>> + struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>>> + struct buffer_head *di_bh = NULL;
>>>>> + struct ocfs2_extent_rec rec;
>>>>> +
>>>>> + if (wait)
>>>>> + ret = ocfs2_inode_lock(inode, &di_bh, 0);
>>>>> + else
>>>>> + ret = ocfs2_try_inode_lock(inode, &di_bh, 0);
>>>>> + if (ret)
>>>>> + goto out;
>>>>> +
>>>>> + if (wait)
>>>>> + down_read(&OCFS2_I(inode)->ip_alloc_sem);
>>>>> + else {
>>>>> + if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
>>>>> + ret = -EAGAIN;
>>>>> + goto out_unlock1;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> + if ((OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) &&
>>>>> + ((map_start + map_len) <= i_size_read(inode)))
>>>>> + goto out_unlock2;
>>>>> +
>>>>> + cpos = map_start >> osb->s_clustersize_bits;
>>>>> + mapping_end = ocfs2_clusters_for_bytes(inode->i_sb,
>>>>> + map_start + map_len);
>>>>> + is_last = 0;
>>>>> + while (cpos < mapping_end && !is_last) {
>>>>> + ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos,
>>>>> + NULL, &rec, &is_last);
>>>>> + if (ret) {
>>>>> + mlog_errno(ret);
>>>>> + goto out_unlock2;
>>>>> + }
>>>>> +
>>>>> + if (rec.e_blkno == 0ULL)
>>>>> + break;
>>>> I think here the blocks is not overwrite, because the hold is found and the
>>>> blocks
>>>> should be allocated.
>>> If the rec.e_blkno == NULL, this means there is a hole.
>>> The file hole means that these blocks are not allocated, it does not like
>> unwritten block.
>>> The unwritten blocks means that these blocks are allocated, but still have
>> not been unwritten.
>>>
>> If we break the loop when we find the hold, out of this function we will
>> allocate the blocks in
>> ocfs2_file_write_iter()->..->ocfs2_direct_IO->__blockdev_direct_IO->..->ocfs2_dio_wr_g
>> et_block()
>> ->ocfs2_write_begin_nolock. Does this violate the semantics of 'IOCB_NOWAIT';
> Yes, then we need to check if this is a overwrite before doing direct-io.
>
I mean here we should return 0 instead of break and we should immediately return -EAGAIN
to upper apps, otherwise, some block allocation will be happen, which violates the
semantics of 'IOCB_NOWAIT'.
Thanks,
Alex
>>
>> BTW, should we consider the down_write() and ocfs2_inode_lock() in
>> ocfs2_dio_wr_get_block() when
>> the flag 'IOCB_NOWAIT' is set;
> I think that we should not consider that layer lock, otherwise, the code change will become more and more complex and big.
> I also refer to ext4 file system code change for this feature(728fbc0e10b7f3ce2ee043b32e3453fd5201c055), they did not do any change in that layer.
>
OK.
> Thanks
> Gang
>
>>
>>>>> +
>>>>> + if (rec.e_flags & OCFS2_EXT_REFCOUNTED)
>>>>> + break;
>>>>> +
>>>>> + cpos = le32_to_cpu(rec.e_cpos) +
>>>>> + le16_to_cpu(rec.e_leaf_clusters);
>>>>> + }
>>>>> +
>>>>> + if (cpos < mapping_end)
>>>>> + ret = 1;
>>>>> +
>>>>> +out_unlock2:
>>>>
>>>> I think the 'out_up_read' is more readable than the 'out_unlock2' .
>>> Ok, I will use more readable tag here.
>>>>
>>>>> + brelse(di_bh);
>>>>> +
>>>>> + up_read(&OCFS2_I(inode)->ip_alloc_sem);
>>>>> +
>>>>> +out_unlock1:
>>>>
>>>> We should release buffer head here.
>>>>
>>>>> + ocfs2_inode_unlock(inode, 0);
>>>>> +
>>>>> +out:
>>>>> + return (ret ? 0 : 1);
>>>>> +}
>>>>> +
>>>>> int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int
>>>> whence)
>>>>> {
>>>>> struct inode *inode = file->f_mapping->host;
>>>>> diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h
>>>>> index 67ea57d..fd9e86a 100644
>>>>> --- a/fs/ocfs2/extent_map.h
>>>>> +++ b/fs/ocfs2/extent_map.h
>>>>> @@ -53,6 +53,9 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64
>>>> v_blkno, u64 *p_blkno,
>>>>> int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>>>> u64 map_start, u64 map_len);
>>>>>
>>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
>>>>> + int wait);
>>>>> +
>>>>> int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int
>>>> origin);
>>>>>
>>>>> int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster,
>>>>>
>>>
>>>
>>> .
>>>
>
> .
>
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