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repoview: fix memory leak of filtered repo classes The leak occurs in long-running server processes with extensions, and is measured at 110kB per request. Before this change, the contents of the `_filteredrepotypes` cache are not properly garbage collected, despite it begin a `WeakKeyDictionary`. Extensions have a tendency to generate a new repository class for each `localrepo` instantiation. Server processes based on `hgwebdir_mod` will instantiate a new `localrepo` for each HTTP request that involves a repository. As a result, with a testing process that repeatedly opens a repository with several extensions activated (`topic` notably among them), we see a steady increase in resident memory of 110kB per repository instantiation before this change. This is also true, if we call `gc.collect()` at each instantiation, like `hgwebdir_mod` does, or not. The cause of the leak is that the *values* aren't weak references. This change uses `weakref.ref` for the values, and this makes in our measurements the resident size increase drop to 5kB per repository instantiation, with no explicit call of `gc.collect()` at all. There is currently no reason to believe that this remaining leak of 5kB is related to or even due to Mercurial core. We've also seen evidence that `ui.ui` instances weren't properly garbage collected before the change (with the change, they are). This could explain why the figures are relatively high. In theory, the collection of weak references could lead to much more misses in the cache, so we measured the impact on the original case that was motivation for introducing that cache in 7e89bd0cfb86 (see also issue5043): `hg convert` of the mozilla-central repository. The bad news here is that there is a major memory leak there, both with and without the present changeset. There were no more cache misses, and we could see no more memory leak with this change: the resident size after importing roughly 100000 changesets was at 12.4GB before, and 12.5GB after. The small increase is mentioned for completeness only, and we believe that it should be ignored, at least as long as the main leak isn't fixed. At less than 1% of the main leak, even finding out whether it is merely noise would be wasteful. Original context where this was spotted and first mitigated: https://foss.heptapod.net/heptapod/heptapod/-/issues/466 The leak reduction was also obtained in Heptapod inner HTTP server, which amounts to the same as `hgwebdir_mod` for these questions. The measurements done with Python 3.9, similar figures seen with 3.8. More work on our side would be needed to give measurements with 2.7, because of testing server process does not support it.
author Georges Racinet <georges.racinet@octobus.net>
date Fri, 23 Apr 2021 18:30:53 +0200
parents 2f7408b7d247
children
line wrap: on
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#require no-chg

  $ send() {
  >   hg --verbose debugwireproto --peer raw http://$LOCALIP:$HGPORT/
  > }

  $ hg init server
  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
  $ cat hg.pid > $DAEMON_PIDS

Request to /api fails unless web.apiserver is enabled

  $ get-with-headers.py $LOCALIP:$HGPORT api
  400 no such method: api
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png" />
  <meta name="robots" content="index, nofollow" />
  <link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>$TESTTMP/server: error</title>
  </head>
  <body>
  
  <div class="container">
  <div class="menu">
  <div class="logo">
  <a href="https://mercurial-scm.org/">
  <img src="/static/hglogo.png" width=75 height=90 border=0 alt="mercurial" /></a>
  </div>
  <ul>
  <li><a href="/shortlog">log</a></li>
  <li><a href="/graph">graph</a></li>
  <li><a href="/tags">tags</a></li>
  <li><a href="/bookmarks">bookmarks</a></li>
  <li><a href="/branches">branches</a></li>
  </ul>
  <ul>
  <li><a href="/help">help</a></li>
  </ul>
  </div>
  
  <div class="main">
  
  <h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
  <h3>error</h3>
  
  
  <form class="search" action="/log">
  
  <p><input name="rev" id="search1" type="text" size="30" value="" /></p>
  <div id="hint">Find changesets by keywords (author, files, the commit message), revision
  number or hash, or <a href="/help/revsets">revset expression</a>.</div>
  </form>
  
  <div class="description">
  <p>
  An error occurred while processing your request:
  </p>
  <p>
  no such method: api
  </p>
  </div>
  </div>
  </div>
  
  
  
  </body>
  </html>
  
  [1]

  $ get-with-headers.py $LOCALIP:$HGPORT api/
  400 no such method: api
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png" />
  <meta name="robots" content="index, nofollow" />
  <link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>$TESTTMP/server: error</title>
  </head>
  <body>
  
  <div class="container">
  <div class="menu">
  <div class="logo">
  <a href="https://mercurial-scm.org/">
  <img src="/static/hglogo.png" width=75 height=90 border=0 alt="mercurial" /></a>
  </div>
  <ul>
  <li><a href="/shortlog">log</a></li>
  <li><a href="/graph">graph</a></li>
  <li><a href="/tags">tags</a></li>
  <li><a href="/bookmarks">bookmarks</a></li>
  <li><a href="/branches">branches</a></li>
  </ul>
  <ul>
  <li><a href="/help">help</a></li>
  </ul>
  </div>
  
  <div class="main">
  
  <h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
  <h3>error</h3>
  
  
  <form class="search" action="/log">
  
  <p><input name="rev" id="search1" type="text" size="30" value="" /></p>
  <div id="hint">Find changesets by keywords (author, files, the commit message), revision
  number or hash, or <a href="/help/revsets">revset expression</a>.</div>
  </form>
  
  <div class="description">
  <p>
  An error occurred while processing your request:
  </p>
  <p>
  no such method: api
  </p>
  </div>
  </div>
  </div>
  
  
  
  </body>
  </html>
  
  [1]

Restart server with support for API server

  $ killdaemons.py
  $ cat > server/.hg/hgrc << EOF
  > [experimental]
  > web.apiserver = true
  > EOF

  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
  $ cat hg.pid > $DAEMON_PIDS

/api lists available APIs (empty since none are available by default)

  $ send << EOF
  > httprequest GET api
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 200 OK\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 100\r\n
  s>     \r\n
  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
  s>     \n
  s>     (no available APIs)\n

  $ send << EOF
  > httprequest GET api/
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api/ HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 200 OK\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 100\r\n
  s>     \r\n
  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
  s>     \n
  s>     (no available APIs)\n

Accessing an unknown API yields a 404

  $ send << EOF
  > httprequest GET api/unknown
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api/unknown HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 404 Not Found\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 33\r\n
  s>     \r\n
  s>     Unknown API: unknown\n
  s>     Known APIs: 

Accessing a known but not enabled API yields a different error

  $ send << EOF
  > httprequest GET api/exp-http-v2-0003
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api/exp-http-v2-0003 HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 404 Not Found\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 33\r\n
  s>     \r\n
  s>     API exp-http-v2-0003 not enabled\n

Restart server with support for HTTP v2 API

  $ killdaemons.py
  $ cat > server/.hg/hgrc << EOF
  > [experimental]
  > web.apiserver = true
  > web.api.http-v2 = true
  > EOF

  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
  $ cat hg.pid > $DAEMON_PIDS

/api lists the HTTP v2 protocol as available

  $ send << EOF
  > httprequest GET api
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 200 OK\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 96\r\n
  s>     \r\n
  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
  s>     \n
  s>     exp-http-v2-0003

  $ send << EOF
  > httprequest GET api/
  >     user-agent: test
  > EOF
  using raw connection to peer
  s> setsockopt(6, 1, 1) -> None (?)
  s>     GET /api/ HTTP/1.1\r\n
  s>     Accept-Encoding: identity\r\n
  s>     user-agent: test\r\n
  s>     host: $LOCALIP:$HGPORT\r\n (glob)
  s>     \r\n
  s> makefile('rb', None)
  s>     HTTP/1.1 200 OK\r\n
  s>     Server: testing stub value\r\n
  s>     Date: $HTTP_DATE$\r\n
  s>     Content-Type: text/plain\r\n
  s>     Content-Length: 96\r\n
  s>     \r\n
  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
  s>     \n
  s>     exp-http-v2-0003