WPA stream_out form & memory consumption

[Richard Biener]

On Tue, Mar 18, 2014 at 4:09 PM, Martin Liška <mliska@suse.cz> wrote:
> Hello,
>    I've been compiling Chromium with LTO and I noticed that WPA stream_out
> forks and do parallel:
> http://gcc.gnu.org/ml/gcc-patches/2013-11/msg02621.html.
>
> I am unable to fit in 16GB memory: ld uses about 8GB and lto1 about 6GB.
> When WPA start to fork, memory consumption increases so that lto1 is killed.
> I would appreciate an --param option to disable this WPA fork. The number of
> forks is taken from build system (-flto=9) which is fine for ltrans phase,
> because LD releases aforementioned 8GB.
>
> What do you think about that?

Hmm, what does cause the memory increase?  Are you eventually
doing garbage collection after the forks in any of the processes?
(just add a global flag may_not_gc_collect and set it to true before
the first fork and assert in ggc_collect () that this flag isn't set)

Richard.

> Thanks,
> Martin