Re: [PATCH RESEND v2 2/2] blk-mq: Avoid memory reclaim when remapping queues

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On 12/06/2016 08:31 AM, Gabriel Krisman Bertazi wrote:
> While stressing memory and IO at the same time we changed SMT settings,
> we were able to consistently trigger deadlocks in the mm system, which
> froze the entire machine.
> 
> I think that under memory stress conditions, the large allocations
> performed by blk_mq_init_rq_map may trigger a reclaim, which stalls
> waiting on the block layer remmaping completion, thus deadlocking the
> system.  The trace below was collected after the machine stalled,
> waiting for the hotplug event completion.
> 
> The simplest fix for this is to make allocations in this path
> non-reclaimable, with GFP_NOIO.  With this patch, We couldn't hit the
> issue anymore.

This looks fine.

-- 
Jens Axboe

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