Re: [PATCH] iommu/iova: silence warnings under memory pressure

[Joe Perches <joe@perches.com>]

On Fri, 2019-11-15 at 15:50 -0500, Qian Cai wrote:
> When running heavy memory pressure workloads, this 5+ old system is
> throwing endless warnings below because disk IO is too slow to recover
> from swapping. Since the volume from alloc_iova_fast() could be large,
> once it calls printk(), it will trigger disk IO (writing to the log
> files) and pending softirqs which could cause a loop and no progress
> from memory reclaim for days.
[]
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
[]
> @@ -233,7 +233,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
>  
>  struct iova *alloc_iova_mem(void)
>  {
> -	return kmem_cache_alloc(iova_cache, GFP_ATOMIC);
> +	return kmem_cache_alloc(iova_cache, GFP_ATOMIC | __GFP_NOWARN);
>  }
>  EXPORT_SYMBOL(alloc_iova_mem);

Is notification ever useful?

If so, maybe something like:

struct iova *alloc_iova_mem(void)
{
	void *mem = kmem_cache_alloc(iova_cache, GFP_ATOMIC | __GFP_NOWARN)_

	WARN_RATELIMIT(!mem, "%s: unable to alloc cache\n", __func__);

	return mem;
}

or maybe use printk_deferred or prink_deferred_once

?