linux-kernel - Re: [PATCH] RAS/CEC: Add debugfs switch to disable at run time

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Message-ID: <20190422171532.GH21457@zn.tnic>
Date:   Mon, 22 Apr 2019 19:15:32 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RAS/CEC: Add debugfs switch to disable at run time

On Mon, Apr 22, 2019 at 03:59:16PM +0000, Luck, Tony wrote:
> > Err, this all sounds to me like the storm detection code should
> > *automatically* disable the CEC in such cases, I'd say.
> 
> Sounds good. But we should distinguish storms that have many different
> addresses from storms that just ping a few addresses.  CEC will see counts
> hit the threshold in the latter case, but it might not be able to take the pages
> offline (because they are locked, or in-use by kernel).
> 
> So I think the change might be to the return value from NOTIFY_STOP to NOTIFY_DONE
> ... but only if we are in the middle of a storm AND the CEC array is full.

Well, regardless of this specific use case, isn't that a generic enough
action that we should do always? I mean, the aspect of falling back to
logging to external agent.

However, currently we don't signal that the CEC is full - we simply
remove the LRU element in cec_add_elem() before we insert the new one.

We can either return a specific retval to say, CEC is full and we had to
delete an elem or we can add a cec_is_full() accessor...

-- 
Regards/Gruss,
    Boris.

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