On Mon, Mar 16, 2015 at 09:37:45PM +0900, Hitoshi Mitake wrote: > On Mon, Mar 16, 2015 at 4:39 PM, Liu Yuan <[email protected]> wrote: > > On Mon, Mar 16, 2015 at 03:55:43PM +0900, Hitoshi Mitake wrote: > >> At Mon, 16 Mar 2015 14:48:47 +0800, > >> Liu Yuan wrote: > >> > > >> > On Mon, Mar 16, 2015 at 03:39:17PM +0900, Hitoshi Mitake wrote: > >> > > At Mon, 16 Mar 2015 14:31:44 +0800, > >> > > Liu Yuan wrote: > >> > > > > >> > > > On Mon, Mar 16, 2015 at 02:08:25PM +0800, Liu Yuan wrote: > >> > > > > On Mon, Mar 16, 2015 at 02:36:57PM +0900, Hitoshi Mitake wrote: > >> > > > > > At Mon, 16 Mar 2015 10:21:50 +0800, > >> > > > > > Liu Yuan wrote: > >> > > > > > > > >> > > > > > > On Thu, Mar 12, 2015 at 08:14:33PM +0900, Hitoshi Mitake wrote: > >> > > > > > > > At Thu, 12 Mar 2015 14:41:56 +0800, > >> > > > > > > > Liu Yuan wrote: > >> > > > > > > > > > >> > > > > > > > > On Tue, Jan 13, 2015 at 10:37:40AM +0900, Hitoshi Mitake > >> > > > > > > > > wrote: > >> > > > > > > > > > Current sheepdog never recycles VIDs. But it will cause > >> > > > > > > > > > problems > >> > > > > > > > > > e.g. VID space exhaustion, too much garbage inode > >> > > > > > > > > > objects. > >> > > > > > > > > > > >> > > > > > > > > > Keeping deleted inode objects is required because living > >> > > > > > > > > > inodes > >> > > > > > > > > > (snapshots or clones) can point objects of the deleted > >> > > > > > > > > > inodes. So if > >> > > > > > > > > > every member of VDI family is deleted, it is safe to > >> > > > > > > > > > remove deleted > >> > > > > > > > > > inode objects. > >> > > > > > > > > > > >> > > > > > > > > > v2: > >> > > > > > > > > > - update test scripts > >> > > > > > > > > > >> > > > > > > > > All the nodes of our test cluster panic out for the > >> > > > > > > > > following problem: > >> > > > > > > > > > >> > > > > > > > > Mar 12 00:05:03 DEBUG [main] zk_handle_notify(1216) NOTIFY > >> > > > > > > > > Mar 12 00:05:03 DEBUG [main] sd_notify_handler(960) op > >> > > > > > > > > NOTIFY_VDI_ADD, size: 96, from: IPv4 ip:192.168.39.177 > >> > > > > > > > > port:7000 > >> > > > > > > > > Mar 12 00:05:03 DEBUG [main] do_add_vdi_state(362) > >> > > > > > > > > 7c2b2b, 3, 0, 22, 0 > >> > > > > > > > > Mar 12 00:05:03 DEBUG [main] do_add_vdi_state(362) > >> > > > > > > > > 7c2b2c, 3, 0, 22, 7c2b2b > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] update_vdi_family(127) > >> > > > > > > > > PANIC: parent VID: 7c2b2b not found > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] crash_handler(286) sheep > >> > > > > > > > > exits unexpectedly (Aborted), si pid 4786, uid 0, errno 0, > >> > > > > > > > > code -6 > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(833) > >> > > > > > > > > sheep.c:288: crash_handler > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(847) > >> > > > > > > > > /lib64/libpthread.so.0() [0x338200f4ff] > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(847) > >> > > > > > > > > /lib64/libc.so.6(gsignal+0x34) [0x3381c328a4] > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(847) > >> > > > > > > > > /lib64/libc.so.6(abort+0x174) [0x3381c34084] > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(833) vdi.c:127: > >> > > > > > > > > update_vdi_family > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(833) vdi.c:398: > >> > > > > > > > > add_vdi_state > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(833) ops.c:711: > >> > > > > > > > > cluster_notify_vdi_add > >> > > > > > > > > Mar 12 00:05:03 EMERG [main] sd_backtrace(833) > >> > > > > > > > > group.c:975: sd_notify_handler > >> > > > > > > > > > >> > > > > > > > > So I tracked back to this patch set. The problem of this > >> > > > > > > > > patch set tried to > >> > > > > > > > > solve is very clear and come along with sheepdog since its > >> > > > > > > > > born. This reveals > >> > > > > > > > > actually the defeciency of our vdi allocation algorithm, > >> > > > > > > > > which we need rethink > >> > > > > > > > > a completely new algorithm to replace it and is not > >> > > > > > > > > fixable, unfortunately. > >> > > > > > > > > > >> > > > > > > > > One simple rule, we can't recyle any vid if it is once > >> > > > > > > > > created because of its > >> > > > > > > > > current hash collision handling. Our current > >> > > > > > > > > implementation forbigs recycling. > >> > > > > > > > > > >> > > > > > > > > Instead of fixing the above panic bug, I'd suggest we > >> > > > > > > > > revert this patch set. > >> > > > > > > > > For the problem this patch set mentioned, I think we need > >> > > > > > > > > a new algoirthm and > >> > > > > > > > > implementation. But before that, we should stay with old > >> > > > > > > > > one, it is stable and > >> > > > > > > > > reliable and should work for small size cluster. > >> > > > > > > > > > >> > > > > > > > > How do you think, Hitoshi and Kazutaka? > >> > > > > > > > > >> > > > > > > > How about providing switch turn on/off VID recycling? e.g. > >> > > > > > > > dog cluster > >> > > > > > > > format --enable-vid-recycle. The code can easily be pushed > >> > > > > > > > into > >> > > > > > > > conditional branches. I can post a patch if this way is good > >> > > > > > > > for you. > >> > > > > > > > > >> > > > > > > > >> > > > > > > This temporary workaroud looks okay but not good enough to me, > >> > > > > > > what I am > >> > > > > > > concerned is that vdi recycle will probably never be > >> > > > > > > implemented if we stick to > >> > > > > > > current vdi allocation algorithm. Once the new vdi allocation > >> > > > > > > is intruduced > >> > > > > > > someday in the future, the new algorithm would have no this > >> > > > > > > kind of problem at > >> > > > > > > all. If this is the case, the above code we leave here is also > >> > > > > > > useless. > >> > > > > > > > >> > > > > > > I think we should focus on the new vdi allocation algorithm, > >> > > > > > > e.g, store > >> > > > > > > {name, vid} directly into a kv engine either implemented by > >> > > > > > > sheep or by with the > >> > > > > > > help of other software like zookeeper. > >> > > > > > > > >> > > > > > > I'm inclined to revert above patch set, for > >> > > > > > > 1. it can't fix a non-fixable problem inherently > >> > > > > > > 2. the code is probalematic and can cause a catastraphic > >> > > > > > > disaster (all node die) > >> > > > > > > 3. we might not need it in the future because it is specific > >> > > > > > > for current vdi > >> > > > > > > allocation algorithm. > >> > > > > > > >> > > > > > We can simply employ whole range lookup of bitmap as a VID > >> > > > > > allocation > >> > > > > > algorithm for recycling policy. Of course it would be harmful for > >> > > > > > snapshot and clone creation, but it can work correctly (and we > >> > > > > > have > >> > > > > > optimization e.g. parallelizing, caching, etc). In addition, the > >> > > > > > performance degradation can happen potentially even if we use the > >> > > > > > existing VID allocation algorithm (e.g. hash collision, although > >> > > > > > course it can happen rearely). > >> > > > > > >> > > > > Do we really need vdi recycle if we bring very complex lines of > >> > > > > code? Current > >> > > > > algorithm can *reuse* of deleted vdi IDs and inodes. So the very > >> > > > > problem is > >> > > > > actually the space effeciency, so you try to reclaim the space > >> > > > > occupied by > >> > > > > deleted vdis. > >> > > > > > >> > > > > If it is very easy to reclaim deleted inodes, I'd say great and > >> > > > > let's go ahead. > >> > > > > But it apparently not. We have this patch set and then the lookup > >> > > > > algorithm is > >> > > > > heavily degrated. > >> > > > > > >> > > > > I'm afraid, lookup the whole range is too costy, considering the > >> > > > > deleted inodes > >> > > > > space we reclaim. I think, most of users can bear the very little > >> > > > > space overhead > >> > > > > for better performance. So this patch set trade the code > >> > > > > complexity and > >> > > > > performance for the space efficiency. Note, we can reclaim inodes > >> > > > > only in the > >> > > > > case that we delete the whole snapshot chain and parent. This is > >> > > > > actually a rare > >> > > > > case. > >> > > > > >> > > > Delete the vdi & snapthos data objects is really good enough to me. > >> > > > Your patch > >> > > > set is the one of efforts to perfect current algorithms. But the > >> > > > cost is too > >> > > > high because the hottest path of vdi_lookup() is heavily degrated > >> > > > for gerenal > >> > > > cases, even though later we can fix all the bugs related to the this > >> > > > patch set. > >> > > > > >> > > > Please consider it. > >> > > > >> > > Of course the increased cost of vdi_lookup() is problem. So I'm > >> > > posting a patch for providing an option for enabling/disabling vid > >> > > recycling. In default, the recycling will be disabled with the > >> > > patch. So users can choose two different policies with different > >> > > pros/cons. > >> > > > >> > > The recycling VID is an actual requirement from the development team > >> > > of NTT DATA. I need to provide it at least as an option. > >> > > >> > THe requrement is for reclaim the deleted inodes? The vid exaustion > >> > problem > >> > mentioned in your patch set, is actually not a problem, no? We can reuse > >> > deleted > >> > inode and vid. If so, reclaim the deleted inodes, which are very little > >> > and > >> > reuable, is so important? > >> > >> The primary problem is VID. But reusing deleted VID correctly will > >> require mucm more complex code e.g. rewriting parent/child > >> relationship (and it would be superset of current code). > > > > I guess so. I don't have a glance of this problem in a code manner, but we > > have > > two state to indicate if the vid is used or not, > > > > 1. bit int bitmap of system_info > > 2. inode's name field > > > > For the non-snapshot case, the valid vid is a) bit is set, b) name is not > > empty. > > So if we zero name, we can resue this bit by check if name is empty. > > > > For the snapshot case, the above criteria still hold true, no? > > > > 001111000 > > ABCD > > > > D is the working vid, ABC are the snapshots. After we remove B, > > > > 0011 11000 > > AB'CD > > > > B' mean its name is empty. So the snapshot chain becomes A->C->D. B is still > > reusable, no? > > > > No. Because C and D can point objects created when B was a working VDI.
You are right, but your patch set won't fix this problem either. I am not concerned this problem, but rather: 1. code complexity and code stability. 2. heavily degraded vdi_lookup(). If we fix one problem by introducing yet another problem(2), I'd suggest we think twice. Yuan -- sheepdog mailing list [email protected] https://lists.wpkg.org/mailman/listinfo/sheepdog
