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

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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Paul E. McKenney 2010-08-13 16:34:22 -07:00
parent a3dc3fb161
commit 5cc6517abd
1 changed files with 15 additions and 6 deletions
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21
Documentation/RCU/checklist.txt
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@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome!
include: include:
a. Keeping a count of the number of data-structure elements a. Keeping a count of the number of data-structure elements
used by the RCU-protected data structure, including those used by the RCU-protected data structure, including
waiting for a grace period to elapse. Enforce a limit those waiting for a grace period to elapse. Enforce a
on this number, stalling updates as needed to allow limit on this number, stalling updates as needed to allow
previously deferred frees to complete. previously deferred frees to complete. Alternatively,
limit only the number awaiting deferred free rather than
the total number of elements.
Alternatively, limit only the number awaiting deferred One way to stall the updates is to acquire the update-side
free rather than the total number of elements. 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 b. Limiting update rate. For example, if updates occur only
once per hour, then no explicit rate limiting is required, once per hour, then no explicit rate limiting is required,