> so lustre_inode_cache is the real culprit when signal_cache appears to > be large. > This cache is slaved on the common inode cache, so there should be one > entry for each lustre inode that is in memory. > These inodes should get pruned when they've been inactive for a while.
What triggers the prunning? >If you look in /proc/sys/fs/inode-nr there should be two numbers: > The first is the total number of in-memory inodes for all filesystems. > The second is the number of "unused" inodes. > > When you write "3" to drop_caches, the second number should drop down to > nearly zero (I get 95 on my desktop, down from 6524). Ok, that is useful to know but echoing 3 to drop_cache or generating memory pressure clears most of the signal_cache (inode) as well as other lustre objects, so this is working fine. The issue that remains is that they are marked as SUnreclaim vs SReclaimable. So i do not think there is a memory leak per se. Regards. Jacek Tomaka On Mon, Apr 29, 2019 at 1:39 PM NeilBrown <[email protected]> wrote: > > Thanks Jacek, > so lustre_inode_cache is the real culprit when signal_cache appears to > be large. > This cache is slaved on the common inode cache, so there should be one > entry for each lustre inode that is in memory. > These inodes should get pruned when they've been inactive for a while. > > If you look in /proc/sys/fs/inode-nr there should be two numbers: > The first is the total number of in-memory inodes for all filesystems. > The second is the number of "unused" inodes. > > When you write "3" to drop_caches, the second number should drop down to > nearly zero (I get 95 on my desktop, down from 6524). > > When signal_cache stays large even after the drop_caches, it suggest > that there are lots of lustre inodes that are thought to be still > active. I'd have to do a bit of digging to understand what that means, > and a lot more to work out why lustre is holding on to inodes longer > than you would expect (if that actually is the case). > > If an inode still has cached data pages attached that cannot easily be > removed, it will not be purged even if it is unused. > So if you see the "unused" number remaining high even after a > "drop_caches", that might mean that lustre isn't letting go of cache > pages for some reason. > > NeilBrown > > > > On Mon, Apr 29 2019, Jacek Tomaka wrote: > > > Wow, Thanks Nathan and NeilBrown. > > It is great to learn about slub merging. It is awesome to have a > > reproducer. > > I am yet to trigger my original problem with slurm_nomerge but > > slabinfo tool (in kernel sources) can actually show merged caches: > > kernel/3.10.0-693.5.2.el7/tools/slabinfo -a > > > > :t-0000112 <- sysfs_dir_cache kernfs_node_cache blkdev_integrity > > task_delay_info > > :t-0000144 <- flow_cache cl_env_kmem > > :t-0000160 <- sigqueue lov_object_kmem > > :t-0000168 <- lovsub_object_kmem osc_extent_kmem > > :t-0000176 <- vvp_object_kmem nfsd4_stateids > > :t-0000192 <- ldlm_resources kiocb cred_jar inet_peer_cache key_jar > > file_lock_cache kmalloc-192 dmaengine-unmap-16 bio_integrity_payload > > :t-0000216 <- vvp_session_kmem vm_area_struct > > :t-0000256 <- biovec-16 ip_dst_cache bio-0 ll_file_data kmalloc-256 > > sgpool-8 filp request_sock_TCP rpc_tasks request_sock_TCPv6 > > skbuff_head_cache pool_workqueue lov_thread_kmem > > :t-0000264 <- osc_lock_kmem numa_policy > > :t-0000328 <- osc_session_kmem taskstats > > :t-0000576 <- kioctx xfrm_dst_cache vvp_thread_kmem > > :t-0001152 <- signal_cache lustre_inode_cache > > > > It is not on a machine that had the problem i described before but the > > kernel version is the same so I am assuming the cache merges are the > same. > > > > Looks like signal_cache points to lustre_inode_cache. > > Regards. > > Jacek Tomaka > > > > > > On Thu, Apr 25, 2019 at 7:42 AM NeilBrown <[email protected]> wrote: > > > >> > >> Hi, > >> you seem to be able to reproduce this fairly easily. > >> If so, could you please boot with the "slub_nomerge" kernel parameter > >> and then reproduce the (apparent) memory leak. > >> I'm hoping that this will show some other slab that is actually using > >> the memory - a slab with very similar object-size to signal_cache that > >> is, by default, being merged with signal_cache. > >> > >> Thanks, > >> NeilBrown > >> > >> > >> On Wed, Apr 24 2019, Nathan Dauchy - NOAA Affiliate wrote: > >> > >> > On Mon, Apr 15, 2019 at 9:18 PM Jacek Tomaka <[email protected]> wrote: > >> > > >> >> > >> >> >signal_cache should have one entry for each process (or > thread-group). > >> >> > >> >> That is what i thought as well, looking at the kernel source, > >> allocations > >> >> from > >> >> signal_cache happen only during fork. > >> >> > >> >> > >> > I was recently chasing an issue with clients suffering from low memory > >> and > >> > saw that "signal_cache" was a major player. But the workload on those > >> > clients was not doing a lot of forking. (and I don't *think* > threading > >> > either) Rather it was a LOT of metadata read operations. > >> > > >> > You can see the symptoms by a simple "du" on a Lustre file system: > >> > > >> > # grep signal_cache /proc/slabinfo > >> > signal_cache 967 1092 1152 28 8 : tunables 0 0 > >> 0 > >> > : slabdata 39 39 0 > >> > > >> > # du -s /mnt/lfs1/projects/foo > >> > 339744908 /mnt/lfs1/projects/foo > >> > > >> > # grep signal_cache /proc/slabinfo > >> > signal_cache 164724 164724 1152 28 8 : tunables 0 0 > >> 0 > >> > : slabdata 5883 5883 0 > >> > > >> > # slabtop -s c -o | head -n 20 > >> > Active / Total Objects (% used) : 3660791 / 3662863 (99.9%) > >> > Active / Total Slabs (% used) : 93019 / 93019 (100.0%) > >> > Active / Total Caches (% used) : 72 / 107 (67.3%) > >> > Active / Total Size (% used) : 836474.91K / 837502.16K (99.9%) > >> > Minimum / Average / Maximum Object : 0.01K / 0.23K / 12.75K > >> > > >> > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > >> > > >> > 164724 164724 100% 1.12K 5883 28 188256K signal_cache > >> > > >> > 331712 331712 100% 0.50K 10366 32 165856K ldlm_locks > >> > > >> > 656896 656896 100% 0.12K 20528 32 82112K kmalloc-128 > >> > > >> > 340200 339971 99% 0.19K 8100 42 64800K kmalloc-192 > >> > > >> > 162838 162838 100% 0.30K 6263 26 50104K osc_object_kmem > >> > > >> > 744192 744192 100% 0.06K 11628 64 46512K kmalloc-64 > >> > > >> > 205128 205128 100% 0.19K 4884 42 39072K dentry > >> > > >> > 4268 4256 99% 8.00K 1067 4 34144K kmalloc-8192 > >> > > >> > 162978 162978 100% 0.17K 3543 46 28344K vvp_object_kmem > >> > > >> > 162792 162792 100% 0.16K 6783 24 27132K > >> kvm_mmu_page_header > >> > > >> > 162825 162825 100% 0.16K 6513 25 26052K sigqueue > >> > > >> > 16368 16368 100% 1.02K 528 31 16896K nfs_inode_cache > >> > > >> > 20385 20385 100% 0.58K 755 27 12080K inode_cache > >> > > >> > > >> > Repeat that for more (and bigger) directories and slab cache added up > to > >> > more than half the memory on this 24GB node. > >> > > >> > This is with CentOS-7.6 and lustre-2.10.5_ddn6. > >> > > >> > I worked around the problem by tackling the "ldlm_locks" memory usage > >> with: > >> > # lctl set_param ldlm.namespaces.lfs*.lru_max_age=10000 > >> > > >> > ...but I did not find a way to reduce the "signal_cache". > >> > > >> > Regards, > >> > Nathan > >> > > > > > > -- > > *Jacek Tomaka* > > Geophysical Software Developer > > > > > > > > > > > > > > *DownUnder GeoSolutions* > > 76 Kings Park Road > > West Perth 6005 WA, Australia > > *tel *+61 8 9287 4143 <+61%208%209287%204143> > > [email protected] > > *www.dug.com <http://www.dug.com>* > -- *Jacek Tomaka* Geophysical Software Developer *DownUnder GeoSolutions* 76 Kings Park Road West Perth 6005 WA, Australia *tel *+61 8 9287 4143 <+61%208%209287%204143> [email protected] *www.dug.com <http://www.dug.com>*
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