Hello Martin,
This exmaple shows why we need to stop merging,
Yes, It's fine since we have "stop merging" in current code.
Regards
Tang
原始邮件
发件人： ＜mwilck@xxxxxxxx＞;
收件人： ＜dm-devel@xxxxxxxxxx＞;
日 期 ：2017年02月20日 19:24
主 题 ：Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices
Hello Tang,
＞ In the second case, we know all events in the sequence have the
＞ same
＞ ＞ WWID; in this case I think it would be safe to filter away "remove"
＞ ＞ events by subsequent "add" events, ending up with "add path1| add
＞ ＞ path2| remove path3". But I may be overlooking something here.
＞
＞ ＞ The dangerous thing if you have simultaneous remove and add events
＞ for
＞ ＞ the same LUN is that processing the "add" events is likely to fail
＞ in
＞ ＞ domap(). If you get "add path1 | remove path2", once you process
＞ "add
＞ ＞ path1", "path2" may not exist in the kernel any more, and "domap"
＞ will
＞ ＞ fail if you try to set up both; you may end up removing the map
＞ ＞ completely. IMHO the only safe way to process events in this
＞ situation
＞ ＞ is to merge the events into a single domap() call.
＞
＞ "case 2: remove path1 |add path1 |remove path2 |add path2 |remove
＞ path3"
＞ Since the mergering is starting from the latest to the eariest
＞ uevent, so the
＞ uevent "remove path3" try to merger other uevents, if we do not stop
＞ mergering,
＞ uevent "remove path3" would merge uevent "remove path2" and uevent
＞ "remove path1". Uevent "add path2" would merge "add path1".
＞ The result is that we get two merged uevents:
＞ 1) add path2, path1
＞ 2) remove path3, path2, path1
＞ Then we process the merged uevents from the earlier to later, We try
＞ to ”add
＞ path2 path1“, and we would create or reload a map device with path1
＞ and path2.
＞ Next we process ” remove path3, path2, path1“, so path1, path2 and
＞ path3 are
＞ all removed from the map device, this is wrong, the correct result
＞ is that the path1
＞ and path2 should be still in the map device.
I don't understand that. This would mean that you'd re-order "remove
path1 | add path1" into "add path1| remove path1", and the same for
path2. That may obviously never happen. Your "stop merging" logic
forbids it, and that's fine for me for now.
Regards
Martin
--
Dr. Martin Wilck ＜mwilck@xxxxxxxx＞, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
＞ In the second case, we know all events in the sequence have the
＞ same
＞ ＞ WWID; in this case I think it would be safe to filter away "remove"
＞ ＞ events by subsequent "add" events, ending up with "add path1| add
＞ ＞ path2| remove path3". But I may be overlooking something here.
＞
＞ ＞ The dangerous thing if you have simultaneous remove and add events
＞ for
＞ ＞ the same LUN is that processing the "add" events is likely to fail
＞ in
＞ ＞ domap(). If you get "add path1 | remove path2", once you process
＞ "add
＞ ＞ path1", "path2" may not exist in the kernel any more, and "domap"
＞ will
＞ ＞ fail if you try to set up both; you may end up removing the map
＞ ＞ completely. IMHO the only safe way to process events in this
＞ situation
＞ ＞ is to merge the events into a single domap() call.
＞
＞ "case 2: remove path1 |add path1 |remove path2 |add path2 |remove
＞ path3"
＞ Since the mergering is starting from the latest to the eariest
＞ uevent, so the
＞ uevent "remove path3" try to merger other uevents, if we do not stop
＞ mergering,
＞ uevent "remove path3" would merge uevent "remove path2" and uevent
＞ "remove path1". Uevent "add path2" would merge "add path1".
＞ The result is that we get two merged uevents:
＞ 1) add path2, path1
＞ 2) remove path3, path2, path1
＞ Then we process the merged uevents from the earlier to later, We try
＞ to ”add
＞ path2 path1“, and we would create or reload a map device with path1
＞ and path2.
＞ Next we process ” remove path3, path2, path1“, so path1, path2 and
＞ path3 are
＞ all removed from the map device, this is wrong, the correct result
＞ is that the path1
＞ and path2 should be still in the map device.
I don't understand that. This would mean that you'd re-order "remove
path1 | add path1" into "add path1| remove path1", and the same for
path2. That may obviously never happen. Your "stop merging" logic
forbids it, and that's fine for me for now.
Regards
Martin
--
Dr. Martin Wilck ＜mwilck@xxxxxxxx＞, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
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