On Thu, Sep 23, 2021 at 12:48 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> Maintain a counter to count allocations that are skipped due to being
> incompatible (oversized, incompatible gfp flags) or no capacity.
>
> This is to compute the fraction of allocations that could not be
> serviced by KFENCE, which we expect to be rare.
>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Acked-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> v2:
> * Do not count deadlock-avoidance skips.
> ---
> mm/kfence/core.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 7a97db8bc8e7..249d75b7e5ee 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -112,6 +112,8 @@ enum kfence_counter_id {
> KFENCE_COUNTER_FREES,
> KFENCE_COUNTER_ZOMBIES,
> KFENCE_COUNTER_BUGS,
> + KFENCE_COUNTER_SKIP_INCOMPAT,
> + KFENCE_COUNTER_SKIP_CAPACITY,
> KFENCE_COUNTER_COUNT,
> };
> static atomic_long_t counters[KFENCE_COUNTER_COUNT];
> @@ -121,6 +123,8 @@ static const char *const counter_names[] = {
> [KFENCE_COUNTER_FREES] = "total frees",
> [KFENCE_COUNTER_ZOMBIES] = "zombie allocations",
> [KFENCE_COUNTER_BUGS] = "total bugs",
> + [KFENCE_COUNTER_SKIP_INCOMPAT] = "skipped allocations (incompatible)",
> + [KFENCE_COUNTER_SKIP_CAPACITY] = "skipped allocations (capacity)",
> };
> static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);
>
> @@ -271,8 +275,10 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g
> list_del_init(&meta->list);
> }
> raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
> - if (!meta)
> + if (!meta) {
> + atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]);
> return NULL;
> + }
>
> if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) {
> /*
> @@ -740,8 +746,10 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
> * Perform size check before switching kfence_allocation_gate, so that
> * we don't disable KFENCE without making an allocation.
> */
> - if (size > PAGE_SIZE)
> + if (size > PAGE_SIZE) {
> + atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);
> return NULL;
> + }
>
> /*
> * Skip allocations from non-default zones, including DMA. We cannot
> @@ -749,8 +757,10 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
> * properties (e.g. reside in DMAable memory).
> */
> if ((flags & GFP_ZONEMASK) ||
> - (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
> + (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) {
> + atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);
> return NULL;
> + }
>
> /*
> * allocation_gate only needs to become non-zero, so it doesn't make
> --
> 2.33.0.464.g1972c5931b-goog
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
