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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-22257] Remove the THP &quot;defrag&quot; startup warning</title>
                <link>https://jira.mongodb.org/browse/SERVER-22257</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;In recent Linux releases it&apos;s enough to turn off THP. Defrag shouldn&apos;t occur if THP is disabled. (rumor has it that it wasn&apos;t completely true in old Linux kernels)&lt;/p&gt;

&lt;p&gt;Acceptance Criteria: completely remove the aforementioned code (with an option to add some documentation regarding Linux Transparent Huge Page defragmentation and its implications to mongod) or update the code appropriately. &lt;/p&gt;</description>
                <environment></environment>
        <key id="259926">SERVER-22257</key>
            <summary>Remove the THP &quot;defrag&quot; startup warning</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-server-servicearch">Backlog - Service Architecture</assignee>
                                    <reporter username="alex.komyagin@mongodb.com">Alexander Komyagin</reporter>
                        <labels>
                    </labels>
                <created>Thu, 21 Jan 2016 15:43:50 +0000</created>
                <updated>Thu, 23 Feb 2023 21:53:32 +0000</updated>
                                                                            <component>Diagnostics</component>
                                        <votes>1</votes>
                                    <watches>14</watches>
                                                                                                                <comments>
                            <comment id="4480262" author="JIRAUSER1263891" created="Wed, 13 Apr 2022 14:41:14 +0000"  >&lt;p&gt;According to &lt;a href=&quot;https://en.wikipedia.org/wiki/Linux_kernel_version_history&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;wikipedia&lt;/a&gt; kernel 3.10 ceased by the second half of 2013. According to &lt;a href=&quot;https://www.mongodb.com/evolved#mdbthreezero&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;MongoDB Version history&lt;/a&gt; that maps to mongo 3.0 (or before) which makes this ticket less relevant nowadays.&lt;/p&gt;

&lt;p&gt;With that said the &lt;a href=&quot;https://github.com/10gen/mongo/blob/master/src/mongo/db/startup_warnings_mongod.cpp#L246-L284&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;code&lt;/a&gt; as it currently stands looks incomplete if compared with &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-22257?focusedCommentId=1155794&amp;amp;page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1155794&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;the previous comment&lt;/a&gt; or even with the document linked hereto and last updated on May 13, 2017: The current code only looks at the synchronous defragmentation. It also runs the risk of misreporting based on different / future kernel versions.&lt;/p&gt;

&lt;p&gt;My suggestion is to, unless these settings are mandatory, deprecate the code and provide the same warnings as some sort of documentation leaving parts of the task to the readers in case they are looking to optimize their deployment. If otherwise these settings are mandatory, then the code should be updated and mongod should gracefully terminate.&lt;/p&gt;</comment>
                            <comment id="4178778" author="JIRAUSER1262719" created="Tue, 9 Nov 2021 20:28:39 +0000"  >&lt;p&gt;We haven&#8217;t heard back from you for some time, so I&#8217;m going to close this ticket. If this is still an issue for you, please provide additional information and we will reopen the ticket.&lt;/p&gt;</comment>
                            <comment id="1870256" author="milkie" created="Fri, 20 Apr 2018 16:58:23 +0000"  >&lt;p&gt;Transferring to platform team, as &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18989&quot; title=&quot;Test for THP is not accurate&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18989&quot;&gt;&lt;del&gt;SERVER-18989&lt;/del&gt;&lt;/a&gt; is related to this and is already on Platform.&lt;/p&gt;</comment>
                            <comment id="1183041" author="martin.bligh" created="Wed, 24 Feb 2016 13:49:42 +0000"  >&lt;p&gt;Seems reasonable though I haven&apos;t checked the details. Also need to be careful of what happens in case they tweak this again in the future I guess.&lt;/p&gt;</comment>
                            <comment id="1182591" author="alex.komyagin@10gen.com" created="Wed, 24 Feb 2016 00:22:25 +0000"  >&lt;p&gt;Or we can just say that for kernels starting with 3.10 for sure &lt;img class=&quot;emoticon&quot; src=&quot;https://jira.mongodb.org/images/icons/emoticons/smile.png&quot; height=&quot;16&quot; width=&quot;16&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt;&lt;/p&gt;</comment>
                            <comment id="1182313" author="martin.bligh" created="Tue, 23 Feb 2016 19:45:09 +0000"  >&lt;p&gt;Sounds like we&apos;d have to work out the exact kernel version where this changed over, including all distro branches, etc, and explain this to the user clearly ... seems like a non-trivial amount of effort&lt;/p&gt;</comment>
                            <comment id="1155726" author="alex.komyagin@10gen.com" created="Wed, 27 Jan 2016 19:47:09 +0000"  >&lt;p&gt;If I&apos;m reading &lt;a href=&quot;https://www.kernel.org/doc/Documentation/vm/transhuge.txt&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://www.kernel.org/doc/Documentation/vm/transhuge.txt&lt;/a&gt; correctly, transparent_hugepage/defrag is responsible for synchronous defrag during huge page allocation:&lt;/p&gt;
&lt;blockquote&gt;
&lt;p&gt;It&apos;s also possible to limit defrag efforts in the VM to generate&lt;br/&gt;
hugepages in case they&apos;re not immediately free to madvise regions or&lt;br/&gt;
to never try to defrag memory and simply fallback to regular pages&lt;br/&gt;
unless hugepages are immediately available.&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;As such, it shouldn&apos;t matter if huge pages are disabled. &lt;/p&gt;

&lt;p&gt;khugepaged/defrag is responsible for async defrag:&lt;/p&gt;
&lt;blockquote&gt;
&lt;p&gt;khugepaged runs usually at low frequency so while one may not want to&lt;br/&gt;
invoke defrag algorithms synchronously during the page faults, it&lt;br/&gt;
should be worth invoking defrag at least in khugepaged.&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;But khugepaged shouldn&apos;t be running if huge pages are disabled:&lt;/p&gt;
&lt;blockquote&gt;
&lt;p&gt;khugepaged will be automatically started when&lt;br/&gt;
transparent_hugepage/enabled is set to &quot;always&quot; or &quot;madvise, and it&apos;ll&lt;br/&gt;
be automatically shutdown if it&apos;s set to &quot;never&quot;.&lt;/p&gt;&lt;/blockquote&gt;</comment>
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            <issuekey id="210879">SERVER-18989</issuekey>
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