On Sat, Nov 15, 2014 at 7:32 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 11/15/2014 12:48 PM, Andrey Korolyov wrote: >> Hello, >> >> I had found recently that the OSD daemons under certain conditions >> (moderate vm pressure, moderate I/O, slightly altered vm settings) can >> go into loop involving isolate_freepages and effectively hit Ceph >> cluster performance. I found this thread > > Do you feel it is a regression, compared to some older kernel version or something? No, it`s just a rare but very concerning stuff. The higher pressure is, the more chance to hit this particular issue, although absolute numbers are still very large (e.g. room for cache memory). Some googling also found simular question on sf: http://serverfault.com/questions/642883/cause-of-page-fragmentation-on-large-server-with-xfs-20-disks-and-ceph but there are no perf info unfortunately so I cannot say if the issue is the same or not. > >> https://lkml.org/lkml/2012/6/27/545, but looks like that the >> significant decrease of bdi max_ratio did not helped even for a bit. >> Although I have approximately a half of physical memory for cache-like >> stuff, the problem with mm persists, so I would like to try >> suggestions from the other people. In current testing iteration I had >> decreased vfs_cache_pressure to 10 and raised vm_dirty_ratio and >> background ratio to 15 and 10 correspondingly (because default values >> are too spiky for mine workloads). The host kernel is a linux-stable >> 3.10. > > Well I'm glad to hear it's not 3.18-rc3 this time. But I would recommend trying > it, or at least 3.17. Lot of patches went to reduce compaction overhead for > (especially for transparent hugepages) since 3.10. Heh, I may say that I limited to pushing knobs in 3.10, because it has a well-known set of problems and any major version switch will lead to months-long QA procedures, but I may try that if none of mine knob selection will help. I am not THP user, the problem is happening with regular 4k pages and almost default VM settings. Also it worth to mean that kernel messages are not complaining about allocation failures, as in case in URL from above, compaction just tightens up to some limit and (after it 'locked' system for a couple of minutes, reducing actual I/O and derived amount of memory operations) it goes back to normal. Cache flush fixing this just in a moment, so should large room for min_free_kbytes. Over couple of days, depends on which nodes with certain settings issue will reappear, I may judge if my ideas was wrong. > >> Non-default VM settings are: >> vm.swappiness = 5 >> vm.dirty_ratio=10 >> vm.dirty_background_ratio=5 >> bdi_max_ratio was 100%, right now 20%, at a glance it looks like the >> situation worsened, because unstable OSD host cause domino-like effect >> on other hosts, which are starting to flap too and only cache flush >> via drop_caches is helping. >> >> Unfortunately there are no slab info from "exhausted" state due to >> sporadic nature of this bug, will try to catch next time. >> >> slabtop (normal state): >> Active / Total Objects (% used) : 8675843 / 8965833 (96.8%) >> Active / Total Slabs (% used) : 224858 / 224858 (100.0%) >> Active / Total Caches (% used) : 86 / 132 (65.2%) >> Active / Total Size (% used) : 1152171.37K / 1253116.37K (91.9%) >> Minimum / Average / Maximum Object : 0.01K / 0.14K / 15.75K >> >> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME >> 6890130 6889185 99% 0.10K 176670 39 706680K buffer_head >> 751232 721707 96% 0.06K 11738 64 46952K kmalloc-64 >> 251636 226228 89% 0.55K 8987 28 143792K radix_tree_node >> 121696 45710 37% 0.25K 3803 32 30424K kmalloc-256 >> 113022 80618 71% 0.19K 2691 42 21528K dentry >> 112672 35160 31% 0.50K 3521 32 56336K kmalloc-512 >> 73136 72800 99% 0.07K 1306 56 5224K Acpi-ParseExt >> 61696 58644 95% 0.02K 241 256 964K kmalloc-16 >> 54348 36649 67% 0.38K 1294 42 20704K ip6_dst_cache >> 53136 51787 97% 0.11K 1476 36 5904K sysfs_dir_cache >> 51200 50724 99% 0.03K 400 128 1600K kmalloc-32 >> 49120 46105 93% 1.00K 1535 32 49120K xfs_inode >> 30702 30702 100% 0.04K 301 102 1204K Acpi-Namespace >> 28224 25742 91% 0.12K 882 32 3528K kmalloc-128 >> 28028 22691 80% 0.18K 637 44 5096K vm_area_struct >> 28008 28008 100% 0.22K 778 36 6224K xfs_ili >> 18944 18944 100% 0.01K 37 512 148K kmalloc-8 >> 16576 15154 91% 0.06K 259 64 1036K anon_vma >> 16475 14200 86% 0.16K 659 25 2636K sigqueue >> >> zoneinfo (normal state, attached) >> > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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