RE: [PATCH] mm/vma: predicate vma_assert_stabilised() on CONFIG_DEBUG_VM

[Seunghyun An]

On Tue, Nov 10, 2026 at 03:10:40PM +0000, Lorenzo Stoakes (ARM) wrote:
> I introduced commit 17fd82c3abe0 ("mm/vma: add and use
> vma_assert_stabilised()") with the intent of picking up programmatic bugs

Tested on an AMD EPYC 9634 (84 cores, 12 CCDs), CONFIG_DEBUG_VM=n.
Applied on d48723711bae; base and patched were measured on the same day.
Throughput figures are in faults/s; JVM pretouch time is in ms.

                              base      patched
  shared-VMA faults, 7 CCDs   1.776M    1.917M   +7.9%
  shared-VMA faults, 12 CCDs  2.303M    2.431M   +5.6%
  pft, 7 CCDs                 1.910M    2.126M  +11.3%
  pft, 84 cores               4.201M    5.028M  +19.7%
  JVM G1 pretouch (32G)       1877 ms   1672 ms -10.9%

Tested-by: Seunghyun An <san55@xxxxxxxx>

As a follow-up, I also checked whether avoiding the __vm_anon_pgoff_hi
read in __folio_set_anon() provides any further benefit. For comparison,
I tested my earlier patch 1 on top, which computes the index from
vm_pgoff for anonymous VMAs and avoids that read:

                              this patch  + patch 1
  shared-VMA faults, 12 CCDs  2.431M      2.941M   +21%
  pft, 12 CCDs                2.434M      3.474M   +43%

With pft on 12 CCDs, this patch alone is essentially unchanged from
base (2.442M faults/s). The additional improvement with patch 1 suggests
that avoiding the __vm_anon_pgoff_hi read may be worth investigating on
CPUs with high coherency costs between L3 cache domains.

Happy to run anything you'd like to try.

Thanks,
Seunghyun