Messages in this thread | | | Date | Fri, 23 Oct 2015 10:33:16 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable() checks |
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On Fri 23-10-15 03:42:26, Tejun Heo wrote: > On Thu, Oct 22, 2015 at 05:49:22PM +0200, Michal Hocko wrote: > > I am confused. What makes rescuer to not run? Nothing seems to be > > hogging CPUs, we are just out of workers which are loopin in the > > allocator but that is preemptible context. > > It's concurrency management. Workqueue thinks that the pool is making > positive forward progress and doesn't schedule anything else for > execution while that work item is burning cpu cycles.
Ohh, OK I can see wq_worker_sleeping now. I've missed your point in other email, sorry about that. But now I am wondering whether this is an intended behavior. The documentation says: WQ_MEM_RECLAIM
All wq which might be used in the memory reclaim paths _MUST_ have this flag set. The wq is guaranteed to have at least one execution context regardless of memory pressure.
Which doesn't seem to be true currently, right? Now I can see your patch to introduce WQ_IMMEDIATE but I am wondering which WQ_MEM_RECLAIM users could do without WQ_IMMEDIATE? I mean all current workers might be looping in the page allocator and it seems possible that WQ_MEM_RECLAIM work items might be waiting behind them so they cannot help to relieve the memory pressure. This doesn't sound right to me. Or I am completely confused and still fail to understand what is WQ_MEM_RECLAIM supposed to be used for. -- Michal Hocko SUSE Labs
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