On 1/23/25 23:44, Christoph Lameter via B4 Relay wrote: > From: Christoph Lameter <cl@xxxxxxxxx> > > KFENCE manages its own pools and redirects regular memory allocations > to those pools in a sporadic way. The usual memory allocator features > like NUMA, memory policies and pfmemalloc are not supported. Can it also violate __GFP_THISNODE constraint? That could be a problem, I recall a problem in the past where it could have been not honoured by the page allocator, leading to corruption of slab lists. > This means that one gets surprising object placement with KFENCE that > may impact performance on some NUMA systems. > > Update the description and make KFENCE depend on VM debugging > having been enabled. > > Signed-off-by: Christoph Lameter <cl@xxxxxxxxx> > --- > Documentation/dev-tools/kfence.rst | 4 +++- > lib/Kconfig.kfence | 10 ++++++---- > 2 files changed, 9 insertions(+), 5 deletions(-) > > diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst > index 541899353865..27150780d6f5 100644 > --- a/Documentation/dev-tools/kfence.rst > +++ b/Documentation/dev-tools/kfence.rst > @@ -8,7 +8,9 @@ Kernel Electric-Fence (KFENCE) is a low-overhead sampling-based memory safety > error detector. KFENCE detects heap out-of-bounds access, use-after-free, and > invalid-free errors. > > -KFENCE is designed to be enabled in production kernels, and has near zero > +KFENCE is designed to be low overhead but does not implememnt the typical > +memory allocation features for its samples like memory policies, NUMA and > +management of emergency memory pools. It has near zero > performance overhead. Compared to KASAN, KFENCE trades performance for > precision. The main motivation behind KFENCE's design, is that with enough > total uptime KFENCE will detect bugs in code paths not typically exercised by > diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence > index 6fbbebec683a..48d2a6a1be08 100644 > --- a/lib/Kconfig.kfence > +++ b/lib/Kconfig.kfence > @@ -5,14 +5,14 @@ config HAVE_ARCH_KFENCE > > menuconfig KFENCE > bool "KFENCE: low-overhead sampling-based memory safety error detector" > - depends on HAVE_ARCH_KFENCE > + depends on HAVE_ARCH_KFENCE && DEBUG_VM > select STACKTRACE > select IRQ_WORK > help > KFENCE is a low-overhead sampling-based detector of heap out-of-bounds > access, use-after-free, and invalid-free errors. KFENCE is designed > - to have negligible cost to permit enabling it in production > - environments. > + to have negligible cost. KFENCE does not support NUMA features > + and other memory allocator features for it sample allocations. > > See <file:Documentation/dev-tools/kfence.rst> for more details. > > @@ -21,7 +21,9 @@ menuconfig KFENCE > detect, albeit at very different performance profiles. If you can > afford to use KASAN, continue using KASAN, for example in test > environments. If your kernel targets production use, and cannot > - enable KASAN due to its cost, consider using KFENCE. > + enable KASAN due to its cost and you are not using NUMA and have > + no use of the memory reserve logic of the memory allocators, > + consider using KFENCE. > > if KFENCE > > > --- > base-commit: d0d106a2bd21499901299160744e5fe9f4c83ddb > change-id: 20250123-kfence_doc_update-93b4576c25bb > > Best regards,
