On Tue, Mar 8, 2022 at 1:20 PM Marco Elver <elver@xxxxxxxxxx> wrote:
Allow the use of a deferrable timer, which does not force CPU wake-ups
when the system is idle. A consequence is that the sample interval
becomes very unpredictable, to the point that it is not guaranteed that
the KFENCE KUnit test still passes.
Nevertheless, on power-constrained systems this may be preferable, so
let's give the user the option should they accept the above trade-off.
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
lib/Kconfig.kfence | 12 ++++++++++++
mm/kfence/core.c | 15 +++++++++++++--
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
index 912f252a41fc..1cf2ea2a1ac7 100644
--- a/lib/Kconfig.kfence
+++ b/lib/Kconfig.kfence
@@ -45,6 +45,18 @@ config KFENCE_NUM_OBJECTS
pages are required; with one containing the object and two adjacent
ones used as guard pages.
+config KFENCE_DEFERRABLE
+ bool "Use a deferrable timer to trigger allocations" if EXPERT
+ help
+ Use a deferrable timer to trigger allocations. This avoids forcing
+ CPU wake-ups if the system is idle, at the risk of a less predictable
+ sample interval.
+
+ Warning: The KUnit test suite fails with this option enabled - due to
+ the unpredictability of the sample interval!
+
+ Say N if you are unsure.
+
config KFENCE_STATIC_KEYS
bool "Use static keys to set up allocations" if EXPERT
depends on JUMP_LABEL
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index f126b53b9b85..451277b41bfb 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -95,6 +95,10 @@ module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_inte
static unsigned long kfence_skip_covered_thresh __read_mostly = 75;
module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644);
+/* If true, use a deferrable timer at the risk of unpredictable sample intervals. */
+static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE);
+module_param_named(deferrable, kfence_deferrable, bool, 0444);
Could you please add a line or two to Documentation/dev-tools/kfence.rst as well?
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Liana Sebastian
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Liana Sebastian
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Diese E-Mail ist vertraulich. Falls Sie diese fälschlicherweise erhalten haben sollten, leiten Sie diese bitte nicht an jemand anderes weiter, löschen Sie alle Kopien und Anhänge davon und lassen Sie mich bitte wissen, dass die E-Mail an die falsche Person gesendet wurde.
This e-mail is confidential. If you received this communication by mistake, please don't forward it to anyone else, please erase all copies and attachments, and please let me know that it has gone to the wrong person.
