<div dir="ltr"><div><div>Despite having 32GB of RAM (and not much swap-space), building a debug version of LLVM + Clang with -j N, and having N > ~10 will make my machine almost stop (to the level where I hit a key and it takes several seconds to respond to that single keypress).<br><br></div>Non-debug builds are much less memory hungry, but of course if you actually want to debug your own code when it crashes inside some LLVM function (becasue you passed in something bad), it is a lot harder. I have both release and debug builds on my machine, for that very reason.<br><br>--<br></div>Mats<br></div><div class="gmail_extra"><br><div class="gmail_quote">On 6 March 2018 at 23:20, via cfe-dev <span dir="ltr"><<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi Chris,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">My experience is that by far the peak memory consumption occurs during linking. Compilations don't use much. And debug configurations seriously increase memory
consumption during linking. This means, perversely, that it's likely faster to do a Release build than a Debug build. I basically never do a Debug build because it takes too long.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I am curious what configuration you used (probably Debug?) and how many parallel threads you had. Because linking is the memory hog, you might try using '-DLLVM_PARALLEL_LINK_JOBS=1'
which might help avoid swapping (which *seriously* slows down a build).<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">HTH,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">--paulr<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">P.S. Yeah, some cautionary words about memory consumption seem like a good idea.
<u></u><u></u></span></p>
<p class="MsoNormal"><a name="m_-4999338149352487362__MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> cfe-dev [mailto:<a href="mailto:cfe-dev-bounces@lists.llvm.org" target="_blank">cfe-dev-bounces@lists.<wbr>llvm.org</a>]
<b>On Behalf Of </b>Chris Moller via cfe-dev<br>
<b>Sent:</b> Tuesday, March 06, 2018 8:38 AM<br>
<b>To:</b> <a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a><br>
<b>Subject:</b> [cfe-dev] newbie<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I just found clang/llvm a few days ago. It looks very cool, but if you don't mind a right-off-the-bat observation, somewhere in the Unix-like build recipe it would be very handy if you'd caution new users about the memory size need to
build clang. My machine has 4GB of RAM and I had another 4GB of swap space--and that wasn't enough. Another 4GB of swap wasn't enough. Ultimately, I had to tick it up to a total of 10GB of swap--monitoring things with the "top" utility, the biggest memory
requirement I saw was just a little short of 11GB.<br>
<br>
In Fedora Linux, it's easy enough to create temporary additional swap spaces, but I've no idea, if it's not the same, how to do that in other distros.<br>
<br>
Anyway, cool stuff, and I'm looking forward to fiddling with it.<u></u><u></u></p>
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