linux-kernel - Re: [RFC PATCH v2 1/3] meminfo_extra: introduce meminfo extra

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Date:   Wed, 25 Mar 2020 21:23:36 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jaewon Kim <jaewon31.kim@...sung.com>, leon@...nel.org,
        vbabka@...e.cz, akpm@...ux-foundation.org, labbott@...hat.com,
        sumit.semwal@...aro.org, minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, kasong@...hat.com,
        bhe@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        jaewon31.kim@...il.com, linux-api@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [RFC PATCH v2 1/3] meminfo_extra: introduce meminfo extra

On Tue, Mar 24, 2020 at 12:46:45PM +0100, Greg KH wrote:
> On Tue, Mar 24, 2020 at 08:37:38PM +0900, Jaewon Kim wrote:
 
> > I don't know other cases in other platform.
> > Not desperately needed but I think we need one userspace knob to see overall hidden huge memory.
> 
> Why?  Who wants that?  What would userspace do with that?  And what
> exactly do you want to show?
> 
> Is this just a debugging thing?  Then use debugfs for that, not proc.

Yes, please use debugfs. Android can ban it in production all at once.

> Isn't that what the DRM developers are starting to do?
> 
> > Additionally I'd like to see all those hidden memory in OutOfMemory log.
> 
> How is anything hidden, can't you see it in the slab information?

There real usecase for something like that is vmware baloon driver.
Two VM instances oversteal pages one from another resulting in guest OOM
which looks like one giant get_free_page() memory leak from inside VM.

I don't know how often this type of issue happens nowadays but countless
OOM support tickets were filed and closed over this nonsense.