linux-kernel - Re: [RFC 19/19] mm, netmem: remove the page pool members in struct page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aCII7vd3C2gB0oi_@casper.infradead.org>
Date: Mon, 12 May 2025 15:42:54 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Byungchul Park <byungchul@...com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kernel_team@...ynix.com, kuba@...nel.org,
	almasrymina@...gle.com, ilias.apalodimas@...aro.org,
	harry.yoo@...cle.com, hawk@...nel.org, akpm@...ux-foundation.org,
	ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
	john.fastabend@...il.com, andrew+netdev@...n.ch,
	edumazet@...gle.com, pabeni@...hat.com, vishal.moola@...il.com
Subject: Re: [RFC 19/19] mm, netmem: remove the page pool members in struct
 page

On Mon, May 12, 2025 at 09:51:03PM +0900, Byungchul Park wrote:
> On Fri, May 09, 2025 at 07:02:30PM +0100, Matthew Wilcox wrote:
> > > +		struct __netmem_desc place_holder_1; /* for page pool */
> > >  		struct {	/* Tail pages of compound page */
> > >  			unsigned long compound_head;	/* Bit zero is set */
> > >  		};
> > 
> > The include and the place holder aren't needed.
> 
> Or netmem_desc overlaying struct page might be conflict with other
> fields of sturct page e.g. _mapcount, _refcount and the like, once the
> layout of struct page *extremly changes* in the future before
> netmem_desc has its own instance.

That's not how it'll happen.  When the layout of struct page changes,
it'll shrink substantially (cut in half).  That means that dynamically
allocating netmem_desc must happen first (along with slab, folio, etc,
etc).