On Wed, Jun 18, 2025 at 07:47:18PM +0530, Dev Jain wrote:
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.
No problem! It's hard to be aware of everything in mm :)
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 : )
I just don't have time right now, I guess I'll have to come back to it later... it's not the end of the world for it to be iffy in my view as long as it passes, but it might just not be of great value.
Philosophically I'd rather we didn't assert internal implementation details like where we place mappings in userland memory. At no point do we promise to not leave larger gaps if we feel like it :)
I'm guessing, reading more, the _real_ test here is some mathematical assertion about layout from HIGH_ADDR_SHIFT -> end of address space when using hints.
But again I'm not sure that achieves much and again also is asserting internal implementation details.
Correct behaviour of this kind of thing probably better belongs to tests in the userland VMA testing I'd say.
Sorry I don't mean to do down work you've done before, just giving an honest technical appraisal!
Anyway don't let this block work to fix the test if it's failing. We can revisit this later.