On 18/06/25 5:27 pm, Lorenzo Stoakes wrote:
On Wed, Jun 18, 2025 at 05:15:50PM +0530, Dev Jain wrote:
On 18/06/25 5:07 pm, Lorenzo Stoakes wrote:
On Wed, Jun 18, 2025 at 04:58:56PM +0530, Dev Jain wrote:
MAP_CHUNK_SIZE was chosen randomly. Good to see it translates into something
logical : )
So I guess I am correct, if we can find two VMAs (except at the edge of the
high addr boundary)
with a gap of greater than MAP_CHUNK_SIZE then there is a bug in mmap().
No haha, not at all!! Firstly fixed addressed override a lot of this, secondly
the 256 page gap (which is configurable btw) is only applicable for mappings
below a stack (in stack grow down arch).
Sorry, I was making that assertion w.r.t this specific selftest. What the test
is doing is exhausting VA space without passing a hint or MAP_FIXED. With this
context, where does this assertion fail? One of them will be if the stack guard
gap is more than 256 pages.
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.
Also, note that the test hasn't reported frequent failures post my change, so
in general settings, w.r.t this test, the assertion experimentally seems to
be true : )
I don't really have time to dig into the test in detail sorry too much else on
at the moment.
But it isn't a big problem even if it happened to turn out that this test isn't
really testing quite what you expected :)
