Hello Eugen. Thank you for the answer. According to knowledge and test results at this issue: https://github.com/ceph/ceph/pull/38574 I've tried their advice and I've applied the following changes. max_mds = 4 standby_mds = 1 mds_cache_memory_limit = 16GB mds_recall_max_caps = 40000 When I set these parameters, 1 day later I saw this log: [8531248.982954] Out of memory: Killed process 1580586 (ceph-mds) total-vm:70577592kB, anon-rss:70244236kB, file-rss:0kB, shmem-rss:0kB, UID:167 pgtables:137832kB oom_score_adj:0 All the MDS services created memory leak and killed by kernel. Because of this I changed it as below and it is stable now but performance is very poor and I still get cache pressure alerts. max_mds = 1 standby_mds = 5 mds_cache_memory_limit = 8GB mds_recall_max_caps = 30000 I'm very surprised that you are advising to decrease "mds_recall_max_caps" because it is the opposite of what developers advised in the issue I've sended. It is very hard to play around with MDS parameters without expert level of understanding what these parameters stands for and how it will effect the behavior. Because of this I'm trying to understand the MDS code flow and I'm very interested with learning more and tuning my system by debugging and understanding my own data flow and MDS usage. I have a very unique data flow and I think I need to configure the system for this case. I have 80+ clients and via all of these clients my users are requesting Read a range of objects and compare them in GPU, they generate new data and Write the new data back in the cluster. So it means my clients usually reads objects only one time and do not read the same object again. Sometimes same user runs multiple service in multiple clients and these services can read the same data from different clients. So having a large cache is useless for my use case. I need to setup MDS and Cephfs Client for this data flow. When I debug the MDS ram usage, I see high allocation all the time and I wonder why? If any of my client does not read any object why MDS does not remove that data from ram allocation? I need to configure MDS for reading the data and removing it very fast if the data is constantly requested from clients. In this case ofc I want a ram cache tier. I'm little confused and I need to learn more about how MDS works and how should I make multiple active MDS faster for my subvolumes and client data flow. Best regards. Eugen Block <eblock@xxxxxx>, 16 Oca 2024 Sal, 11:36 tarihinde şunu yazdı: > Hi, > > I have dealt with this topic multiple times, the SUSE team helped > understanding what's going on under the hood. The summary can be found > in this thread [1]. > > What helped in our case was to reduce the mds_recall_max_caps from 30k > (default) to 3k. We tried it in steps of 1k IIRC. So I suggest to > reduce that value step by step (maybe start with 20k or something) to > find the optimal value. > > Regards, > Eugen > > [1] https://www.spinics.net/lists/ceph-users/msg73188.html > > Zitat von Özkan Göksu <ozkangksu@xxxxxxxxx>: > > > Hello. > > > > I have 5 node ceph cluster and I'm constantly having "clients failing to > > respond to cache pressure" warning. > > > > I have 84 cephfs kernel clients (servers) and my users are accessing > their > > personal subvolumes located on one pool. > > > > My users are software developers and the data is home and user data. > (Git, > > python projects, sample data and generated new data) > > > > > --------------------------------------------------------------------------------- > > --- RAW STORAGE --- > > CLASS SIZE AVAIL USED RAW USED %RAW USED > > ssd 146 TiB 101 TiB 45 TiB 45 TiB 30.71 > > TOTAL 146 TiB 101 TiB 45 TiB 45 TiB 30.71 > > > > --- POOLS --- > > POOL ID PGS STORED OBJECTS USED %USED MAX > AVAIL > > .mgr 1 1 356 MiB 90 1.0 GiB 0 30 > TiB > > cephfs.ud-data.meta 9 256 69 GiB 3.09M 137 GiB 0.15 45 > TiB > > cephfs.ud-data.data 10 2048 26 TiB 100.83M 44 TiB 32.97 45 > TiB > > > --------------------------------------------------------------------------------- > > root@ud-01:~# ceph fs status > > ud-data - 84 clients > > ======= > > RANK STATE MDS ACTIVITY DNS INOS DIRS > > CAPS > > 0 active ud-data.ud-04.seggyv Reqs: 142 /s 2844k 2798k 303k > > 720k > > POOL TYPE USED AVAIL > > cephfs.ud-data.meta metadata 137G 44.9T > > cephfs.ud-data.data data 44.2T 44.9T > > STANDBY MDS > > ud-data.ud-02.xcoojt > > ud-data.ud-05.rnhcfe > > ud-data.ud-03.lhwkml > > ud-data.ud-01.uatjle > > MDS version: ceph version 17.2.6 > (d7ff0d10654d2280e08f1ab989c7cdf3064446a5) > > quincy (stable) > > > > > ----------------------------------------------------------------------------------- > > My MDS settings are below: > > > > mds_cache_memory_limit | 8589934592 > > mds_cache_trim_threshold | 524288 > > mds_recall_global_max_decay_threshold | 131072 > > mds_recall_max_caps | 30000 > > mds_recall_max_decay_rate | 1.500000 > > mds_recall_max_decay_threshold | 131072 > > mds_recall_warning_threshold | 262144 > > > > > > I have 2 questions: > > 1- What should I do to prevent cache pressue warning ? > > 2- What can I do to increase speed ? > > > > - Thanks > > _______________________________________________ > > ceph-users mailing list -- ceph-users@xxxxxxx > > To unsubscribe send an email to ceph-users-leave@xxxxxxx > > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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