cull 2% more in each run (to compensate for new files being added)

If each Cull operation attempts to reach exactly BRUN / FRUN, it will
fail to meet that goal because new files are being added during the
Cull, and another Cull will be started right after that, which will
again fail to meet the goal, leaving the daemon in an endless culling
loop.

Adding 2% to the configured BRUN / FRUN values is an experiment to see
whether this solves the loop.

Author: MaxKellermann

debian/changelog

@@ -1,5 +1,6 @@
 cm4all-cash (0.7) unstable; urgency=low
 
+  * cull 2% more in each run (to compensate for new files being added)
   * switch to C++23
   * require Meson 1.2 (for C++23 support)
 

src/Main.cxx

@@ -51,10 +51,23 @@ OpenDevCachefiles(const Config &config)
 	return fd;
 }
 
+/**
+ * Add 2% to the configured BRUN / FRUN values to compensate for files
+ * being added while we're culling.
+ *
+ * If each Cull operation attempts to reach exactly BRUN / FRUN, it
+ * will fail to meet that goal because new files are being added
+ * during the Cull, and another Cull will be started right after that,
+ * which will again fail to meet the goal, leaving the daemon in an
+ * endless culling loop.
+ */
+static constexpr uint_least8_t RUN_PERCENT_OFFSET = 2;
+
 inline
 Instance::Instance(const Config &config)
 	:dev_cachefiles(event_loop, OpenDevCachefiles(config), BIND_THIS_METHOD(OnCull)),
-	 brun(config.brun), frun(config.frun),
+	 brun(config.brun + RUN_PERCENT_OFFSET),
+	 frun(config.frun + RUN_PERCENT_OFFSET),
 	 culling_disabled(config.culling_disabled)
 {
 	event_loop.EnableUring(16384, IORING_SETUP_SINGLE_ISSUER|IORING_SETUP_COOP_TASKRUN);