Re: [PATCH v5 3/3] kselftest: mm: introduce alloc_isolated_mem()

On 9/10/26 13:22, Yeoreum Yun wrote:

quoted

On Thu, Sep 10, 2026 at 01:14:42PM +0200, David Hildenbrand (Arm) wrote:

quoted

On 9/10/26 13:02, Yeoreum Yun wrote:

quoted

Since there is no interface to get vm_flags not via /proc/self/smaps,
It might be good to have it for preventing unwanted VMA merge.

And might be useful for future to prevent unwated VMA merge.

See my reply on why vm flags are generally not a problem. Just like other
properties that are not changed during VMA merging.

Let's not perform random code changes without a clear picture.

And just to emphasize again: VMA merging could already be a problem before
memalign() internal changes.

(also observe here how we do a MADV_HUGEPAGE, so this is all rather arbitrary,
which is not good)

As I mentioned in my previous reply, what I’m trying to prevent here is
a failure when checking, immediately after memory allocation,
that a specific vm_flag is not set.

Yes, I agree that this could have been a problem even before
the internal changes to memalign(). An unwanted VMA merge could already
occur at the time of memory allocation.

So what I’m trying to avoid is a test failure where, due to such an
unexpected VMA merge during allocation, the subsequent check that
a specific vm_flag is not present fails.

Which is only a guard-region marker problem?

Yes. so if we remove ASSERT_FALSE(check_vmflag_guard(ptr)), TBH
we don't need this patch unless other usage comes up to prevent unwanted
VMA merge.

Would it be better to drop ASSERT_FALSE(check_vmflag_guard(ptr)) in
guard test?

-- 
Sincerely,
Yeoreum Yun