On Mon, Mar 16, 2015 at 4:39 PM, Liu Yuan <namei.u...@gmail.com> 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. Thanks, Hitoshi -- sheepdog mailing list sheepdog@lists.wpkg.org https://lists.wpkg.org/mailman/listinfo/sheepdog