rcu: document ways of stalling updates in low-memory situations

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 16 insertions, 7 deletions

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index c7c6788956f4..0c134f8afc6f 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome!
         include:
 
         a.      Keeping a count of the number of data-structure elements
-                used by the RCU-protected data structure, including those
-                waiting for a grace period to elapse.  Enforce a limit
-                on this number, stalling updates as needed to allow
-                previously deferred frees to complete.
-
-                Alternatively, limit only the number awaiting deferred
-                free rather than the total number of elements.
+                used by the RCU-protected data structure, including
+                those waiting for a grace period to elapse.  Enforce a
+                limit on this number, stalling updates as needed to allow
+                previously deferred frees to complete.  Alternatively,
+                limit only the number awaiting deferred free rather than
+                the total number of elements.
+
+                One way to stall the updates is to acquire the update-side
+                mutex.  (Don't try this with a spinlock -- other CPUs
+                spinning on the lock could prevent the grace period
+                from ever ending.)  Another way to stall the updates
+                is for the updates to use a wrapper function around
+                the memory allocator, so that this wrapper function
+                simulates OOM when there is too much memory awaiting an
+                RCU grace period.  There are of course many other
+                variations on this theme.
 
         b.      Limiting update rate.  For example, if updates occur only
                 once per hour, then no explicit rate limiting is required,