linux-kernel - Re: [patch] mm, show_mem: suppress page counts in non-blockable contexts

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Message-ID: <alpine.DEB.2.02.1302271413460.7155@chino.kir.corp.google.com>
Date:	Wed, 27 Feb 2013 14:16:07 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] mm, show_mem: suppress page counts in non-blockable
 contexts

On Wed, 27 Feb 2013, Michal Hocko wrote:

> But we are trying to prevent from soft lockups by calling
> touch_nmi_watchdog every now when iterating over pages so the lock up
> detector shouldn't trigger.
> 
> Anyway, I think that the additional information (which can be really
> costly as you are describing) is not that useful. Most of the useful
> information is already printed by show_free_areas. Or does it help when
> we know how much memory is shared/reserved/etc. when the allocation
> fails?
> 

I do not think it is helpful since show_free_areas() already shows all 
pertinent information, and hence I'm suppressing it in atomic contexts in 
this patch.

> So I do agree with the dropping the additional information for the
> allocation failure path (sysrq+m might still show it) but I fail to see
> how the lockup detector plays any role here. Can we just drop it because
> it is not that interesting and it is costly so it is not worth
> bothering?
>  

I would agree it is not interesting to debugging VM issues and is 
obviously very expensive.
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