From: Marco Elver <elver@xxxxxxxxxx> Subject: kfence: add note to documentation about skipping covered allocations Add a note briefly mentioning the new policy about "skipping currently covered allocations if pool close to full." Since this has a notable impact on KFENCE's bug-detection ability on systems with large uptimes, it is worth pointing out the feature. Link: https://lkml.kernel.org/r/20210923104803.2620285-5-elver@xxxxxxxxxx Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Acked-by: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Aleksandr Nogikh <nogikh@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Taras Madan <tarasmadan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/dev-tools/kfence.rst | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/Documentation/dev-tools/kfence.rst~kfence-add-note-to-documentation-about-skipping-covered-allocations +++ a/Documentation/dev-tools/kfence.rst @@ -269,6 +269,17 @@ tail of KFENCE's freelist, so that the l first, and the chances of detecting use-after-frees of recently freed objects is increased. +If pool utilization reaches 75% (default) or above, to reduce the risk of the +pool eventually being fully occupied by allocated objects yet ensure diverse +coverage of allocations, KFENCE limits currently covered allocations of the +same source from further filling up the pool. The "source" of an allocation is +based on its partial allocation stack trace. A side-effect is that this also +limits frequent long-lived allocations (e.g. pagecache) of the same source +filling up the pool permanently, which is the most common risk for the pool +becoming full and the sampled allocation rate dropping to zero. The threshold +at which to start limiting currently covered allocations can be configured via +the boot parameter ``kfence.skip_covered_thresh`` (pool usage%). + Interface --------- _
