linux-kernel - Re: [PATCH] dma-debug: Make things less spammy under memory pressure

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Message-ID: <CAF6AEGuMN23hxe1+PES-F0rgXDnxi48OfbdHKasPGVnbFvQ8rw@mail.gmail.com>
Date:   Tue, 31 May 2022 15:19:45 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "open list:DMA MAPPING HELPERS" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH] dma-debug: Make things less spammy under memory pressure

On Tue, May 31, 2022 at 3:00 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2022-05-31 22:51, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Ratelimit the error msg to avoid flooding the console.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >   kernel/dma/debug.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> > index f8ff598596b8..683966f0247b 100644
> > --- a/kernel/dma/debug.c
> > +++ b/kernel/dma/debug.c
> > @@ -564,7 +564,7 @@ static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs)
> >
> >       rc = active_cacheline_insert(entry);
> >       if (rc == -ENOMEM) {
> > -             pr_err("cacheline tracking ENOMEM, dma-debug disabled\n");
> > +             pr_err_ratelimited("cacheline tracking ENOMEM, dma-debug disabled\n");
> >               global_disable = true;
>
> Given that it's supposed to disable itself entirely if it ever gets
> here, just how spammy is it exactly?

um, quite..  tbf that was in the context of a WIP igt test for
shrinker which was trying to cycle thru ~2x RAM size worth of GEM
buffers on something like 72 threads.  So it could just be threads
that had gotten past the dma_debug_disabled() check already before
global_disable was set to true?

I guess this could be pr_err_once() instead, then?

BR,
-R

> Thanks,
> Robin.
>
> >       } else if (rc == -EEXIST && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)) {
> >               err_printk(entry->dev, entry,