linux-kernel - Re: [PATCH v2] iommu/iova: silence warnings under memory pressure

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Date:   Fri, 22 Nov 2019 11:46:58 -0500
From:   Qian Cai <cai@....pw>
To:     Joe Perches <joe@...ches.com>, jroedel@...e.de
Cc:     baolu.lu@...ux.intel.com, dwmw2@...radead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/iova: silence warnings under memory pressure

On Fri, 2019-11-22 at 08:28 -0800, Joe Perches wrote:
> On Fri, 2019-11-22 at 09:59 -0500, Qian Cai wrote:
> > On Thu, 2019-11-21 at 20:37 -0800, Joe Perches wrote:
> > > On Thu, 2019-11-21 at 21:55 -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 an infinite loop and make
> > > > no progress for days by the ongoimng memory reclaim. This is the counter
> > > > part for Intel where the AMD part has already been merged. See the
> > > > commit 3d708895325b ("iommu/amd: Silence warnings under memory
> > > > pressure"). Since the allocation failure will be reported in
> > > > intel_alloc_iova(), so just call printk_ratelimted() there and silence
> > > > the one in alloc_iova_mem() to avoid the expensive warn_alloc().
> > > 
> > > []
> > > > v2: use dev_err_ratelimited() and improve the commit messages.
> > > 
> > > []
> > > > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > > 
> > > []
> > > > @@ -3401,7 +3401,8 @@ static unsigned long intel_alloc_iova(struct device *dev,
> > > >  	iova_pfn = alloc_iova_fast(&domain->iovad, nrpages,
> > > >  				   IOVA_PFN(dma_mask), true);
> > > >  	if (unlikely(!iova_pfn)) {
> > > > -		dev_err(dev, "Allocating %ld-page iova failed", nrpages);
> > > > +		dev_err_ratelimited(dev, "Allocating %ld-page iova failed",
> > > > +				    nrpages);
> > > 
> > > Trivia:
> > > 
> > > This should really have a \n termination on the format string
> > > 
> > > 		dev_err_ratelimited(dev, "Allocating %ld-page iova failed\n",
> > > 
> > > 
> > 
> > Why do you say so? It is right now printing with a newline added anyway.
> > 
> >  hpsa 0000:03:00.0: DMAR: Allocating 1-page iova failed
> 
> If another process uses pr_cont at the same time,
> it can be interleaved.

I lean towards fixing that in a separate patch if ever needed, as the origin
dev_err() has no "\n" enclosed either.