From 5cc6517abdeccb6690b344a43b5ce8eaee82da3c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Aug 2010 16:34:22 -0700 Subject: [PATCH] rcu: document ways of stalling updates in low-memory situations Signed-off-by: Paul E. McKenney --- Documentation/RCU/checklist.txt | 23 ++++++++++++++++------- 1 file 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, -- 2.20.1