linux-kernel - [PATCH 3/3] kfence: add note to documentation about skipping covered allocations

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Message-Id: <20210917110756.1121272-3-elver@google.com>
Date:   Fri, 17 Sep 2021 13:07:56 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com
Subject: [PATCH 3/3] 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.

Signed-off-by: Marco Elver <elver@...gle.com>
---
 Documentation/dev-tools/kfence.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst
index 0fbe3308bf37..e698234999d6 100644
--- a/Documentation/dev-tools/kfence.rst
+++ b/Documentation/dev-tools/kfence.rst
@@ -269,6 +269,14 @@ tail of KFENCE's freelist, so that the least recently freed objects are reused
 first, and the chances of detecting use-after-frees of recently freed objects
 is increased.
 
+If pool utilization reaches 75% or above, to reduce the probability of the pool
+containing ~100% allocated objects yet ensure diverse coverage of allocations,
+KFENCE limits currently covered allocations of the same source from further
+filling up the pool. A side-effect is that this also limits frequent long-lived
+allocations of the same source filling up the pool permanently, thereby
+reducing the risk of the pool becoming full and the sampled allocation rate
+dropping to zero.
+
 Interface
 ---------
 
-- 
2.33.0.464.g1972c5931b-goog