Re: [PATCH 1/6] mm/selftests: Fix virtual_address_range test issues.

[Dev Jain <dev.jain@arm.com>]

On 18/06/25 7:37 pm, Lorenzo Stoakes wrote:
> On Wed, Jun 18, 2025 at 07:28:16PM +0530, Dev Jain wrote:
>> On 18/06/25 5:27 pm, Lorenzo Stoakes wrote:
>>> On Wed, Jun 18, 2025 at 05:15:50PM +0530, Dev Jain wrote:
>>> Are you accounting for sys.max_map_count? If not, then you'll be hitting that
>>> first.
>> run_vmtests.sh will run the test in overcommit mode so that won't be an issue.
> Umm, what? You mean overcommit all mode, and that has no bearing on the max
> mapping count check.
>
> In do_mmap():
>
> 	/* Too many mappings? */
> 	if (mm->map_count > sysctl_max_map_count)
> 		return -ENOMEM;
>
>
> As well as numerous other checks in mm/vma.c.

Ah sorry, didn't look at the code properly just assumed that overcommit_always meant overriding
this.

>
> I'm not sure why an overcommit toggle is even necessary when you could use
> MAP_NORESERVE or simply map PROT_NONE to avoid the OVERCOMMIT_GUESS limits?
>
> I'm pretty confused as to what this test is really achieving honestly. This
> isn't a useful way of asserting mmap() behaviour as far as I can tell.

Well, seems like a useful way to me at least : ) Not sure if you are in the mood
to discuss that but if you'd like me to explain from start to end what the test
is doing, I can do that : )