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authorMarco Elver <elver@google.com>2021-11-05 23:45:37 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-06 23:30:43 +0300
commit5cc906b4b4a510b274113ddb3f88d60644553f79 (patch)
treef044488fbfa53b5fcad9ca70979b77ddd9f4a87b /Documentation
parent08f6b10630f284755087f58aa393402e15b92977 (diff)
downloadlinux-5cc906b4b4a510b274113ddb3f88d60644553f79.tar.xz
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@google.com Signed-off-by: Marco Elver <elver@google.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Alexander Potapenko <glider@google.com> Cc: Aleksandr Nogikh <nogikh@google.com> Cc: Jann Horn <jannh@google.com> Cc: Taras Madan <tarasmadan@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/dev-tools/kfence.rst11
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst
index 0fbe3308bf37..d45f952986ae 100644
--- a/Documentation/dev-tools/kfence.rst
+++ b/Documentation/dev-tools/kfence.rst
@@ -269,6 +269,17 @@ 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% (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
---------