[v4] ceph: defer flushing the capsnap if the Fb is used

From: Xiubo Li <xiubli@redhat.com>

If the Fb cap is used it means the current inode is flushing the
dirty data to OSD, just defer flushing the capsnap.

URL: https://tracker.ceph.com/issues/48679
URL: https://tracker.ceph.com/issues/48640
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---

V4:
- Fix stuck issue when running the snaptest-git-ceph.sh pointed by Jeff.

V3:
- Add more comments about putting the inode ref
- A small change about the code style

V2:
- Fix inode reference leak bug


 fs/ceph/caps.c | 33 ++++++++++++++++++++-------------
 fs/ceph/snap.c | 10 ++++++++++
 2 files changed, 30 insertions(+), 13 deletions(-)

On 2021/2/2 23:59, Jeff Layton wrote:
> On Tue, 2021-02-02 at 14:54 +0800, xiubli@redhat.com wrote:
>> From: Xiubo Li <xiubli@redhat.com>
>>
>> If the Fb cap is used it means the current inode is flushing the
>> dirty data to OSD, just defer flushing the capsnap.
>>
>> URL: https://tracker.ceph.com/issues/48679
>> URL: https://tracker.ceph.com/issues/48640
>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>> ---
>>
>> V4:
>> - Fix stuck issue when running the snaptest-git-ceph.sh pointed by Jeff.
>>
>> V3:
>> - Add more comments about putting the inode ref
>> - A small change about the code style
>>
>> V2:
>> - Fix inode reference leak bug
>>
>>
>>   fs/ceph/caps.c | 33 ++++++++++++++++++++-------------
>>   fs/ceph/snap.c | 10 ++++++++++
>>   2 files changed, 30 insertions(+), 13 deletions(-)
>>
>> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
>> index abbf48fc6230..570731c4d019 100644
>> --- a/fs/ceph/caps.c
>> +++ b/fs/ceph/caps.c
>> @@ -3047,6 +3047,7 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
>>   {
>>   	struct inode *inode = &ci->vfs_inode;
>>   	int last = 0, put = 0, flushsnaps = 0, wake = 0;
>> +	bool check_flushsnaps = false;
>>   
>>
>>   	spin_lock(&ci->i_ceph_lock);
>>   	if (had & CEPH_CAP_PIN)
>> @@ -3063,26 +3064,17 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
>>   	if (had & CEPH_CAP_FILE_BUFFER) {
>>   		if (--ci->i_wb_ref == 0) {
>>   			last++;
>> +			/* put the ref held by ceph_take_cap_refs() */
>>   			put++;
>> +			check_flushsnaps = true;
>>   		}
>>   		dout("put_cap_refs %p wb %d -> %d (?)\n",
>>   		     inode, ci->i_wb_ref+1, ci->i_wb_ref);
>>   	}
>> -	if (had & CEPH_CAP_FILE_WR)
>> +	if (had & CEPH_CAP_FILE_WR) {
>>   		if (--ci->i_wr_ref == 0) {
>>   			last++;
>> -			if (__ceph_have_pending_cap_snap(ci)) {
>> -				struct ceph_cap_snap *capsnap =
>> -					list_last_entry(&ci->i_cap_snaps,
>> -							struct ceph_cap_snap,
>> -							ci_item);
>> -				capsnap->writing = 0;
>> -				if (ceph_try_drop_cap_snap(ci, capsnap))
>> -					put++;
>> -				else if (__ceph_finish_cap_snap(ci, capsnap))
>> -					flushsnaps = 1;
>> -				wake = 1;
>> -			}
>> +			check_flushsnaps = true;
>>   			if (ci->i_wrbuffer_ref_head == 0 &&
>>   			    ci->i_dirty_caps == 0 &&
>>   			    ci->i_flushing_caps == 0) {
>> @@ -3094,6 +3086,21 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
>>   			if (!__ceph_is_any_real_caps(ci) && ci->i_snap_realm)
>>   				drop_inode_snap_realm(ci);
>>   		}
>> +	}
>> +	if (check_flushsnaps && __ceph_have_pending_cap_snap(ci)) {
>> +		struct ceph_cap_snap *capsnap =
>> +			list_last_entry(&ci->i_cap_snaps,
>> +					struct ceph_cap_snap,
>> +					ci_item);
>> +
>> +		capsnap->writing = 0;
>> +		if (ceph_try_drop_cap_snap(ci, capsnap))
>> +			/* put the ref held by ceph_queue_cap_snap() */
>> +			put++;
>> +		else if (__ceph_finish_cap_snap(ci, capsnap))
>> +			flushsnaps = 1;
>> +		wake = 1;
>> +	}
>>   	spin_unlock(&ci->i_ceph_lock);
>>   
>>
>>   	dout("put_cap_refs %p had %s%s%s\n", inode, ceph_cap_string(had),
>> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
>> index b611f829cb61..0728b01d4d43 100644
>> --- a/fs/ceph/snap.c
>> +++ b/fs/ceph/snap.c
>> @@ -623,6 +623,16 @@ int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
>>   		return 0;
>>   	}
>>   
>>
>> +	/* Fb cap still in use, delay it */
>> +	if (ci->i_wb_ref) {
>> +		dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu "
>> +		     "used WRBUFFER, delaying\n", inode, capsnap,
>> +		     capsnap->context, capsnap->context->seq,
>> +		     ceph_cap_string(capsnap->dirty), capsnap->size);
>> +		capsnap->writing = 1;
>> +		return 0;
>> +	}
>> +
>>   	ci->i_ceph_flags |= CEPH_I_FLUSH_SNAPS;
>>   	dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu\n",
>>   	     inode, capsnap, capsnap->context,
> Much better. This one seems to behave better. I've gone ahead and taken
> this into testing branch.

Sure, thanks.

BRs

> Thanks!