{"id":813,"date":"2016-06-01T18:48:02","date_gmt":"2016-06-01T18:48:02","guid":{"rendered":"http:\/\/nenadnoveljic.com\/blog\/?p=813"},"modified":"2018-05-17T16:13:16","modified_gmt":"2018-05-17T16:13:16","slug":"solaris-11-3-hang-kernel-object-manager","status":"publish","type":"post","link":"https:\/\/nenadnoveljic.com\/blog\/solaris-11-3-hang-kernel-object-manager\/","title":{"rendered":"Solaris 11.3 Hangs Because of Kernel Object Manager"},"content":{"rendered":"<p>I started occasionally hitting\u00a0a hanging issue lasting for approximately\u00a0two minutes after upgrading to Solaris 11.3.<\/p>\n<p>There is extensive <em>kmem_task<\/em> acitivity just before the hang which I recorded with the following DTrace script:<\/p>\n<pre><code>\r\n#!\/usr\/sbin\/dtrace\r\nprofile:::profile-997Hz\r\n\/ execname == \"kmem_task\" \/\r\n{\r\n@[stack()] = count() ;\r\n}\r\n\r\nprofile:::tick-1s\r\n{\r\nprintf(\"\\n\\n%Y\\n\",walltimestamp);\r\nprinta(\"%k %@d\\n\",@);\r\ntrunc(@);\r\n}\r\n\r\n[...truncated...]\r\n\r\n<span style=\"color: #ff0000;\">genunix`kom_cachetag_destructor+0x27<\/span>\r\ngenunix`kmem_magazine_destroy+0x67\r\ngenunix`kmem_depot_ws_reap+0x77\r\ngenunix`kmem_cache_reap+0x76\r\ngenunix`kmem_do_processing+0x28\r\ngenunix`kmem_async+0x159\r\ngenunix`kmem_sysdc_pinit+0x9f\r\nunix`thread_start+0x8\r\n\r\n168<\/code><\/pre>\n<p>Note: I keep eye on <em>kmem_task<\/em> because I&#8217;ve already discovered\u00a0<a href=\"http:\/\/nenadnoveljic.com\/blog\/arc-resizing-user_reserve_hint_pct\/\" target=\"_blank\">another performance problem<\/a> caused by this process.<\/p>\n<p><em>kom_cachetag_destructor<\/em>, the last function on the stack, is the part of the new kernel memory allocation mechanism, Kernel Object Manager (KOM) which has been introduced in Solaris 11.3 (see\u00a0<a href=\"https:\/\/support.oracle.com\/epmos\/faces\/DocumentDisplay?_afrLoop=361468357408792&amp;id=1430323.1&amp;_adf.ctrl-state=huhohtqjh_757\" target=\"_blank\">Metalink note 1430323.1 How to Understand ZFS File Data Value by mdb and ZFS ARC Size<\/a> ).<\/p>\n<p>Therefore I started to collect the performance data related to <em>kom.<\/em> Below is the snapshotted data just before and after the freeze:<\/p>\n<pre><code>kstat -c kom_class<u><\/u><u><\/u>\r\n\r\n[...truncated...]\r\n\r\nmodule: genunix instance: 1\r\nname: arc_data class: kom_class\r\ncrtime 1434292.13355787\r\n<span style=\"color: #ff0000;\">defrag_freed 102481<\/span>\r\n<span style=\"color: #ff0000;\">defrag_nomem 52794<\/span>\r\n<span style=\"color: #ff0000;\">defrag_partial 974<\/span>\r\n<span style=\"color: #ff0000;\">defrag_skipped 37792<\/span>\r\nmem_in_use 300896756224\r\nmem_total 302138785792\r\nsnaptime 1575865.05633055<u><\/u><u><\/u>\r\n\r\n[...truncated...]\r\n\r\nmodule: genunix instance: 1\r\nname: arc_data class: kom_class\r\ncrtime 1434292.13355787\r\n<span style=\"color: #ff0000;\">defrag_freed 181442<\/span>\r\n<span style=\"color: #ff0000;\">defrag_nomem 219274<\/span>\r\n<span style=\"color: #ff0000;\">defrag_partial 980<\/span>\r\n<span style=\"color: #ff0000;\">defrag_skipped 179675<\/span>\r\nmem_in_use 136538190336\r\nmem_total 136616869888\r\nsnaptime 1575889.24564696\r\n\r\n[...truncated...]<\/code><\/pre>\n<p>It can be seen that<em> kmem_task\u00a0<\/em>performs some defragmentation when the problem happens.<\/p>\n<p>The bug described in the <a href=\"https:\/\/support.oracle.com\/epmos\/faces\/DocumentDisplay?_afrLoop=361931059996243&amp;id=2129106.1&amp;_adf.ctrl-state=huhohtqjh_874\" target=\"_blank\">Metalink Doc ID 2129106.1 &#8220;arc_throttle causes heavy fragmentation on KOM slabs leading to hangs&#8221;<\/a>\u00a0has\u00a0similar symptoms.<\/p>\n<p>This is still work in progress. I&#8217;ll keep updating the blog post with relevant information, so stay tuned!<\/p>\n<p><strong>Update on 20. June 2016:<\/strong><\/p>\n<p>Oracle delivered an IDR patch containing the fixes for the following bugs, which completely resolved the issue:<\/p>\n<ul>\n<li>22347071 KOM fragmentation issue<\/li>\n<li>21748206 KOM defrag goes off the rails when ARC throttles under heavy I\/O load<\/li>\n<li>23005679 KOM vacate has several rare race conditions<\/li>\n<li>18507051 Can&#8217;t boot systems with more than 100 cpus after tuning segkmem_lpsize<\/li>\n<li>23340416 KOM slab double free in capture<\/li>\n<\/ul>\n<p>The bug fixes are not downloadable via Metalink, but you can get them by requesting an IDR from Oracle Support which I highly recommend to do if you&#8217;re on Solaris 11.3.<\/p>\n<p>For the final fix Solaris engineering is targeting SRU 11 at the moment.<\/p>\n<p><strong>Update on 1. December 2016<\/strong><\/p>\n<p>The above mentioned patches resolved the hanging issue completely. However, we still occasionally see some IO outliers caused by reaping ZFS ARC. Recently, Oracle published the Metalink note <a href=\"https:\/\/support.oracle.com\/epmos\/faces\/DocumentDisplay?id=2205638.1\" target=\"_blank\">Solaris 11.3: kmem cache reaping of buffers with large number of entries can lead to long delays which could cause Cluster node eviction (Doc ID 2205638.1)<\/a> which relates to the problem. If you&#8217;ve found the information in this blog post useful, you might also be interested in <a href=\"http:\/\/nenadnoveljic.com\/blog\/arc-resizing-user_reserve_hint_pct\/\" target=\"_blank\">ZFS ARC Resizing (user_reserve_hint_pct)<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>The blog post describes a hanging issue which occurs after upgrading to Solaris 11.3. The problem is caused by the new kernel memory allocation mechanism. <a href=\"https:\/\/nenadnoveljic.com\/blog\/solaris-11-3-hang-kernel-object-manager\/\" class=\"more-link\">Continue Reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[24,19,14],"tags":[],"class_list":["post-813","post","type-post","status-publish","format-standard","hentry","category-dtrace","category-kmem_task","category-solaris"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Solaris 11.3 Hangs Because of Kernel Object Manager - All-round Database Topics<\/title>\n<meta name=\"description\" content=\"Solaris 11.3 hanging issue because of the Kernel Object Manager\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/nenadnoveljic.com\/blog\/solaris-11-3-hang-kernel-object-manager\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Solaris 11.3 Hangs Because of Kernel Object Manager - 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