http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50636
Bug #: 50636
Summary: GC in large LTO builds cause excessive fragmentation
in memory map
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: andi-...@firstfloor.org
When doing a very large LTO build I fail with "out of virtual memory"
Some investigation showed the problem was not actually running out of
memory, but gcc excessively fragmenting its memory map. The Linux kernel
has a default limit of 64k mappings per process and the fragmentation
exceeded that. This lead to gc mmap allocations failing and other problems.
A workaround is to increase /proc/sys/vm/max_map_count
Looking at /proc/$(pidof lto1)/maps I see there are lots of 1-3 page holes
between other anonymousmemory. I think that's caused by ggc-pages free_pages()
function freeing too early and in too small chunks
(and perhaps LTO garbage collecting too much?)
