Memory use during build

[htot]

What is the problem this feature will solve?

My build machine is 8 cores / 16 threads. It has 16GB RAM. If I build with make -j 16 the compile stage takes about 30 min. But during link 5 executables are being linked simultaneously, each taking 4GB RAM. Disk thrashing starts and the link phase takes an extreme long time to complete. In the mean while keyboard/mouse stop responding.

Alternative I can set make -j 2 in which case the compile phase takes multiple hours.

I would like only one executable linked at a time, but compiling to respect 16 threads.

What is the feature you are proposing to solve the problem?

Possibly a hard coded limit in the makefile. Or a command line switch.

What alternatives have you considered?

Other then buying more RAM, I can send SIGSTOP from over ssh (seems to respond better then local terminal). The stopped linkers are swapped out and not swapped back in. Then I can SIGCONT one by one. This works but requires manual intervention.

[aduh95]

I'm personally always doing make -j12 on my 16 core machine, so I can keep using it while it compiles.

[htot]

I bet you have a bit more RAM?

[bnoordhuis]

But during link 5 executables are being linked simultaneously, each taking 4GB RAM.

You can serialize them with flock(1):

$ make -j16 LINK='flock /tmp g++' LINK.host='flock /tmp g++'

LINK.host is only necessary when cross-compiling - edit: probably a good idea to include anyway

[htot]

I'm using Yocto recipe, let's see if I can force that to use flock, thanks for the tip!

[htot]

@bnoordhuis that is brilliant. Thank you!. The yocto recipe already has:

EXTRA_OEMAKE = "\
    CC.host='${CC}' \
    CFLAGS.host='${CPPFLAGS} ${CFLAGS}' \
    CXX.host='${CXX}' \
    CXXFLAGS.host='${CPPFLAGS} ${CXXFLAGS}' \
    LDFLAGS.host='${LDFLAGS}' \
    AR.host='${AR}' \
    \
    builddir_name=./ \
"

I inserted LINK.host='flock /tmp ${CXX}' \ as that seemed most logical, but that didn't help a bit (the 4 calls in my log to flock were never simultaneous). However after changing it to LINK='flock /tmp ${CXX}' \ it works.

This makes an enormous difference in my Yocto image build time (nodejs was the dominant factor).