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

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Date:   Fri, 15 Nov 2019 13:13:03 -0800
From:   Joe Perches <joe@...ches.com>
To:     Qian Cai <cai@....pw>, jroedel@...e.de
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/iova: silence warnings under memory pressure

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

?