Re: [Ocfs2-devel] [PATCH v2 2/2] ocfs2: add trimfs lock to avoid duplicated trims in cluster

[Changwei Ge]

On 2018/1/4 10:09, Gang He wrote:
> Hi Alex,
> 
> 
>>>>
>> Hi Gang,
>>
>> On 2017/12/14 13:14, Gang He wrote:
>>> As you know, ocfs2 has support trim the underlying disk via
>>> fstrim command. But there is a problem, ocfs2 is a shared disk
>>> cluster file system, if the user configures a scheduled fstrim
>>> job on each file system node, this will trigger multiple nodes
>>> trim a shared disk simultaneously, it is very wasteful for CPU
>>> and IO consumption, also might negatively affect the lifetime
>>> of poor-quality SSD devices.
>>> Then, we introduce a trimfs dlm lock to communicate with each
>>> other in this case, which will make only one fstrim command to
>>> do the trimming on a shared disk among the cluster, the fstrim
>>> commands from the other nodes should wait for the first fstrim
>>> to finish and returned success directly, to avoid running a the
>>> same trim on the shared disk again.
>>>
>> For the same purpose, can we take global bitmap meta lock EXMODE instead of
>> add a new trimfs dlm lock?
> I do not think using EXMODE lock to global bitmap meta can handle this case.
> this patch's purpose is to avoid duplicated trim when the nodes in cluster are configured to a schedule fstrim (usually the administrator do like that).
> But, there are lots of path to use EXMODE lock to global bitmap meta, we can not know which is used to trim fs.
> Second, we can not use global bitmap meta lock to save fstrim related data and trylock.

Adding a new type of lock resource is acceptable, I suppose.

Thanks,
Changwei

> 
> Thanks
> Gang
> 
>>
>> Thanks,
>> Alex
>>
>>> Compare with first version, I change the fstrim commands' returned
>>> value and behavior in case which meets a fstrim command is running
>>> on a shared disk.
>>>
>>> Signed-off-by: Gang He <ghe@xxxxxxxx>
>>> ---
>>>   fs/ocfs2/alloc.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>>>   1 file changed, 44 insertions(+)
>>>
>>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>>> index ab5105f..5c9c3e2 100644
>>> --- a/fs/ocfs2/alloc.c
>>> +++ b/fs/ocfs2/alloc.c
>>> @@ -7382,6 +7382,7 @@ int ocfs2_trim_fs(struct super_block *sb, struct
>> fstrim_range *range)
>>>   	struct buffer_head *gd_bh = NULL;
>>>   	struct ocfs2_dinode *main_bm;
>>>   	struct ocfs2_group_desc *gd = NULL;
>>> +	struct ocfs2_trim_fs_info info, *pinfo = NULL;
>>>   
>>>   	start = range->start >> osb->s_clustersize_bits;
>>>   	len = range->len >> osb->s_clustersize_bits;
>>> @@ -7419,6 +7420,42 @@ int ocfs2_trim_fs(struct super_block *sb, struct
>> fstrim_range *range)
>>>   
>>>   	trace_ocfs2_trim_fs(start, len, minlen);
>>>   
>>> +	ocfs2_trim_fs_lock_res_init(osb);
>>> +	ret = ocfs2_trim_fs_lock(osb, NULL, 1);
>>> +	if (ret < 0) {
>>> +		if (ret != -EAGAIN) {
>>> +			mlog_errno(ret);
>>> +			ocfs2_trim_fs_lock_res_uninit(osb);
>>> +			goto out_unlock;
>>> +		}
>>> +
>>> +		mlog(ML_NOTICE, "Wait for trim on device (%s) to "
>>> +		     "finish, which is running from another node.\n",
>>> +		     osb->dev_str);
>>> +		ret = ocfs2_trim_fs_lock(osb, &info, 0);
>>> +		if (ret < 0) {
>>> +			mlog_errno(ret);
>>> +			ocfs2_trim_fs_lock_res_uninit(osb);
>>> +			goto out_unlock;
>>> +		}
>>> +
>>> +		if (info.tf_valid && info.tf_success &&
>>> +		    info.tf_start == start && info.tf_len == len &&
>>> +		    info.tf_minlen == minlen) {
>>> +			/* Avoid sending duplicated trim to a shared device */
>>> +			mlog(ML_NOTICE, "The same trim on device (%s) was "
>>> +			     "just done from node (%u), return.\n",
>>> +			     osb->dev_str, info.tf_nodenum);
>>> +			range->len = info.tf_trimlen;
>>> +			goto out_trimunlock;
>>> +		}
>>> +	}
>>> +
>>> +	info.tf_nodenum = osb->node_num;
>>> +	info.tf_start = start;
>>> +	info.tf_len = len;
>>> +	info.tf_minlen = minlen;
>>> +
>>>   	/* Determine first and last group to examine based on start and len */
>>>   	first_group = ocfs2_which_cluster_group(main_bm_inode, start);
>>>   	if (first_group == osb->first_cluster_group_blkno)
>>> @@ -7463,6 +7500,13 @@ int ocfs2_trim_fs(struct super_block *sb, struct
>> fstrim_range *range)
>>>   			group += ocfs2_clusters_to_blocks(sb, osb->bitmap_cpg);
>>>   	}
>>>   	range->len = trimmed * sb->s_blocksize;
>>> +
>>> +	info.tf_trimlen = range->len;
>>> +	info.tf_success = (ret ? 0 : 1);
>>> +	pinfo = &info;
>>> +out_trimunlock:
>>> +	ocfs2_trim_fs_unlock(osb, pinfo);
>>> +	ocfs2_trim_fs_lock_res_uninit(osb);
>>>   out_unlock:
>>>   	ocfs2_inode_unlock(main_bm_inode, 0);
>>>   	brelse(main_bm_bh);
>>>
> 
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