[LTP] [PATCH] mmap_24-1: Change vm.max_map_count if needed

[Martin Doucha]

On 09. 05. 25 6:03, Li Wang wrote:
> There aremany ways toavoid OOM (e.g., overcommit_memory, oom_score_adj,
> ulimit, etc.). However, the purpose of the mmap_24-1.c test is to 
> exhaust thevirtual
> address space and trigger ENOMEM.
> 
> Limiting vm.max_map_count may prevent OOM, but it changes the failure 
> cause to
> hitting themap count limit, not actual address space exhaustion, which 
> might be away
> from thetest's intent.
> 
> Iguess using setrlimit(RLIMIT_AS, ...) is more appropriate here, as it 
> enforces address
> space limits while preserving the original test goal.

64bit address space is so large that exhausting it requires 512+GB of 
page table structures alone (for the 48bit variant). And kernel will not 
return ENOMEM when it runs out of free memory for pagetable structures, 
it'll trigger OOM.

The mmap_24-1 test started failing after the default vm.max_map_count 
increased in one of our tested product so this is the limit we want to 
change here. But you could copy the test and change RLIMIT_AS there. 
That would also be a valid test case.

-- 
Martin Doucha   mdoucha@suse.cz
SW Quality Engineer
SUSE LINUX, s.r.o.
CORSO IIa
Krizikova 148/34
186 00 Prague 8
Czech Republic