linux-kernel - Re: [PATCH] /dev/zero: make private mapping full anonymous mapping

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Message-ID: <e7dbc60a-490e-a55d-8476-9ce9bcee7bed@gentwo.org>
Date: Wed, 15 Jan 2025 14:05:42 -0800 (PST)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Yang Shi <yang@...amperecomputing.com>
cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, arnd@...db.de, 
    gregkh@...uxfoundation.org, Liam.Howlett@...cle.com, vbabka@...e.cz, 
    jannh@...gle.com, willy@...radead.org, liushixin2@...wei.com, 
    akpm@...ux-foundation.org, linux-mm@...ck.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH] /dev/zero: make private mapping full anonymous mapping

On Wed, 15 Jan 2025, Yang Shi wrote:

>
> > > I just thought of named anonymous VMA may help. We can give the private
> > > /dev/zero mapping a name, for example, just "/dev/zero". However,
> > > "[anon:/dev/zero]" will show up in smaps/maps. We can't keep the device
> > > numbers and inode number either, but it seems it can tell the user this
> > > mapping comes from /dev/zero, and it also explicitly tells us it is
> > > specially treated by kernel. Hopefully setting anon_name is permitted.
> > But then that'd require CONFIG_ANON_VMA_NAME unfortunately :(
>
> Yes.

Add a counter for NULL pages in smaps?

I.e.

Null:	  4 kB

Both anonymous and file mappings could have NULL page references right?