Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable() checks

[Christoph Lameter]

On Thu, 22 Oct 2015, Tejun Heo wrote:

> The only way to hang the execution for a work item w/ WQ_MEM_RECLAIM
> is to create a cyclic dependency on another work item and keep that
> work item busy wait.  Workqueue thinks that work item is making
> progress as it's running and doesn't schedule the next one.
>
> (I was misremembering here) HIGHPRI originally was implemented
> head-queueing on the same pool followed by immediate execution, so
> could get around cases where this could happen, but that got lost
> while converting it to a separate pool.  I can introduce another flag
> to bypass concurrency management if necessary (it's kinda trivial) but
> busy-waiting cyclic dependency is a pretty unusual thing.
>
> If this is actually a legit busy-waiting cyclic dependency, just let
> me know.

There is no dependency of the vmstat updater on anything.
They can run anytime. If there is a dependency then its created by the
kworker subsystem itself.


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