On Sun, Aug 11, 2019 at 10:36 AM <mcatanzaro(a)gnome.org> wrote:

I think this is an overwhelmingly important point, and as somebody regularly working with ARM machines with tiny amounts of RAM, it is of considerable interest to me.

I typically use CentOS because stability is important to me, but most worthwhile things filter to there, so I hope what I'm about to say is not _too_ deprecated.

1) Compile options

From what I can tell from rpm macro options, default on C7 seems to be -O2. -Os seems to help in most cases.

Adding -ffunction-sections -fdata-sections to defaults can help considerably in producing smaller binaries, and is not the default.

Linking with -Wl,--gc-sections helps a lot and is not the default

Extensive stripping seems to already be the default (--strip-unneeded, removal of .comment and .note sections)

2) Runtime condiguration

Default stack size is 8192 (ulimit -s). This unnecessarily eats a considerably amount of memory. I have yet to see anything that actually experiences problems with 1M.

3) zram

This was mentioned earlier in the thread, and on most of my systems, memory constrained or otherwise, unless I have an overwhelming reason not to, I run with zram swap equal in size to RAM with lz4 compression and vm.swappiness=100. I typically see compression ratios between 2:1 and 3:1 in zram, so on a system with, say, 10GB of RAM, it would provide 10GB of very fast swap at a cost of 3-5GB of RAM. This seems like a favourable trade off, especially on systems with extremely constrained RAM (e.g. ARM devices with 512MB of RAM).

I'm sure there is more that can be done, but this seems like a good start as far as the cost / benefit is concerned.